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IC 


8948 



Bureau of Mines Information Circular/1983 



Back Injuries 



Proceedings: Bureau of Mines Technology Transfer 
Symposia, Pittsburgh, PA, August 9, 1983, 
and Reno, NV, August 15, 1983 



Compiled by James M. Peay 




UNITED STATES DEPARTMENT OF THE INTERIOR 



'p^ / h '' ^ t-h, . ^MMMi 'Y lt»^); 



Information Circular 8948 



Back Injuries 



Proceedings: Bureau of Mines Technology Transfer 
Symposia, Pittsburgh, PA, August 9, 1983, 
and Reno, NV, August 15, 1983 



Compiled by James M. Peay 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 






c\'0 



%^ 



^1^ 




This publication has been cataloged as follows: 



Bureau of 


Mines T 


echnology Transfer 


Sympos 


ia (1983 : 


Pittsburgh, PA, 


and Reno, N 


V) 








Back inj 


uries. 












(Bureau 


oi Mines in 


ormation circu 


ar ; 


8948) 






Includes 


bibliograpl 


ical references 


. 








Supt. of Docs, no.: 


28.27:8948. 










1. Mine accidents 
Clongrcsscs. I. Peay, 
circular (United States. 


-Congresses. 2. 
James M. 11. Tit 
Bureau of Mines) ; 


Back- 
e. Ill 
8948. 


-Wounds 
. Series: 


and injuries- 
Information 


TN295.U4 


fTNSll] 


622s [622' 


.8] 


83-600258 





CONTENTS 

Page 

Abs tract 1 

Introduction 2 

Materials Handling Methods and Problems in Underground Coal Mines , by 

Richard L. Unger and Daniel J. Connelly 3 

Activities and Objects Most Commonly Associated With Underground Coal Miners' 

Back Injuries, by Robert H. Peters 23 

Analysis of Coal Mining Back Injury Statistics, by Terrence J. Stobbe and 

Ralph W. Plummer 32 

Two Back Risks in Mining: Lifting and Pushing and Pulling, by Robert 0. Andres 41 
Field Testing of Workers Involved in Material Handling, by BCarl H. E. Kroemer.. 47 
Lifting Capacity Determination, by M. M. Ayoub, J. L. Selan, W. Karwowski, and 

H. P. R. Rao 54 

Job Design for Manual Material Handling Tasks, by M. M. Ayoub, J. L. Selan, and 

H. P. R. Rao 64 

Back Injuries and Maintenance Material Handling in Low-Seam Coal Mines , by 

Ernest J. Conway and William W. Elliott 74 

Training Procedures to Reduce Low Back Injuries , by Nancy C. Selby 81 

A Manual Materials Handling (MMH) Training Program for the Mining Industry, by 

Daniel J. Connelly 88 

Mechanization of Materials Handling Tasks , by Richard L. Unger 102 



BACK INJURIES 

Proceedings: Bureau of Mines Technology Transfer Symposia, Pittsburgh, PA, 
August 9, 1983, and Reno, NV, August 15, 1983 

Compiled by James M, Peay 



ABSTRACT 

These proceedings consist of papers presented at two Bureau of Mines 
Technology Transfer symposia on reducing back injuries in the mining in- 
dustry. The sjnnposia were held in August 1983 and covered a wide range 
of topics related to a more fundamental understanding of factors that 
lead to back, injuries and approaches for reducing the frequency and 
severity of such injuries. 

'Supervisory engineering psychologist, Pittsburgh Research Center, Bureau of Mines, 
Pittsburgh, PA. 



INTRODUCTION 



Back injuries constitute the largest 
single category of lost-time accidents in 
the mining industry. U.S. Department of 
Labor [Health and Safety Analysis Center 
(HSAC)] data for 1981 indicates there 
were 37,017 accidents in the mining in- 
dustry of which approximately 25 pet or 
roughly 9,254 incidents involved back in- 
juries. Back injuries of the most severe 
nature, i.e., strains, sprains, and dis- 
located disks accounted for 5,458 inci- 
dents or approximately 15 pet of all min- 
ing injuries. 

In addition, this category of injury 
accounts for more lost workdays than any 
other single type of injury. For exam- 
ple, 40 pet of the lost-time back inju- 
ries incurred by underground coal miners 
during 1981 resulted in the miner missing 
more than 4 weeks of work. When the num- 
ber of lost workdays per back injury in- 
cident is compared with other types of 
mining injuries, statistics indicate that 
on the average, those workers experi- 
encing back injuries are off the job ap- 
proximately 6 days longer. Thus, back 
injuries not only constitute the single 
largest category of mining injuries, but 
also lead in degree of severity as re- 
flected in lost workdays. 

Back injuries, therefore, represent not 
only a tremendous economic cost to coal 
companies, to miners and their families, 
and to society, they also represent a 
tremendous amount of human suffering. 
Data and expert optinion are in agreement 
that intensified efforts and new ap- 
proaches to reducing back injuries are 
called for. 

As pointed out by Robert H. Peters' 
paper in these proceedings, there are 
many good reasons to believe that the 



mining environmental conditions and cur- 
rent work procedures, which involve con- 
siderable manual materials handling 
tasks, pose relatively unique barriers to 
preventing back injuries. Compared with 
most other types of industrial settings, 
many mines, especially underground opera- 
tions, require considerable manual lift- 
ing of heavy materials. Also, compared 
with most other types of industrial set- 
tings, many underground coal mines have 
less than desirable illumination, are 
wetter, and have constricted work spaces. 
Illumination and water problems can re- 
sult in back injuries caused by slipping 
on wet or muddy surfaces or by tripping 
over things that cannot be easily seen. 
The thickness of many mineral seams also 
prevents miners from performing work 
while standing erect, forcing miners to 
perform heavy work while in stooped or 
kneeling positions, thus placing signifi- 
cantly more stress on their backs than 
other industrial workers who can perform 
lifting activites while standing erect. 

Training miners to cope with existing 
work conditions has been the traditional 
approach to reducing back injuries, how- 
ever this method has many deficiencies, 
as reflected in the continuing high fre- 
quency and severity rates. While im- 
proved training should be continued, 
newly developed selection procedures and 
extensive job redesign based on bio- 
mechanical and ergonomic studies appear 
to offer the greatest potential for fu- 
ture positive impact. Many of the papers 
contained in these proceedings, there- 
fore, focus on assessment and selection 
of workers who are most capable of per- 
forming heavy lifting tasks and on analy- 
sis and design of mining jobs to elimi- 
nate many hazards that eventually lead to 
back injuries. 



MATERIALS HANDLING METHODS AND PROBLEMS IN UNDERGROUND COAL MINES 
By Richard L. Ungerl and Daniel J. Connelly2 

ABSTRACT 



Materials handling accidents are the 
leading cause of nonfatal injuries in 
underground coal mines in the United 
States. The Bureau of Mines has spon- 
sored research into the problems asso- 
ciated with materials handling in 



underground coal mines. This paper pro- 
vides descriptions of the methods, exam- 
ples of activities, flow paths of materi- 
als, problem areas, and accident analyses 
of materials handling operations reported 
in Bureau of Mines research studies. 



INTRODUCTION 



Annually, materials handling is the 
leading accident classification in under- 
ground coal mines in the United States. 
In 1980, materials handling accidents 
accounted for 34% of the 15,075 nonfatal 
days-lost accidents in underground coal 
mines. 

In order to identify the various fac- 
tors that characterize the materials 
handling problem, several analyses are 
necessary. Bureau of Mines sponsored 



research projects3 have provided a better 
understanding of materials handling acci- 
dents in underground coal mines. The 
information reported in this paper is a 
result of those research efforts. The 
descriptions of materials handling meth- 
ods, flow patterns, commonly handled ma- 
terials, problems of mine environment and 
personnel, and accident analyses that are 
presented define the hazards associated 
with materials handling in underground 
coal mines. 



BREAKDOWN OF THE OPERATING ENVIRONMENT 



Manual handling of materials in an un- 
derground coal mine can be described as 
the performance of actions on items in 
various operating environments. The 
operating environments can be described 
by the associated mine activities, loca- 
tion, space limitations, and usage. A 
practical division of the operating en- 
vironments has been defined by handling 

^Civil engineer. 

^Safety specialist. 
Both authors are 
Pittsburgh Research 
Mines, Pittsburgh, PA. 

■^Diaz, R. A., and A. 
tem for Handling Supplies in Underground 
Coal Mines ongoing BuMines contract 
H0188049; for inf., contact G. R. Bock- 
osh, TPO, Pittsburgh Res. Center, Pitts- 
burgh, PA. 

Foote, A. L. , and J. S. Schaefer. 
Mine Materials Handling Vehicle (MMHV) 
(contract H0242015 MBAssociates) . Bu- 
Mines OFR 59-80, 1978', 308 pp.; NTIS PB 
80-178890. 



employed by the 
Center, Bureau of 

D. Chitaley. Sys- 



functions which describe the general pur- 
pose of the activities. 4 These handling 
functions are 

1. Production end use . 5 This function 
relates to the handling of items during 
their end use at the working face. Some 
work activity examples are 

Erecting temporary curtains for 
ventilation. 

Rock dusting. 

Roof bolting. 

Erecting roof timbers. 

^First work cited in footnote 3. 

^The end use handling associated with 
section move, mine maintenance, and 
equipment maintenance is included in the 
respective functions. End use handling 
associated with the production handling 
function is classified as a separate 
function. 



2. Production supply . This function 
relates to the handling of materials from 
the surface yard to locations near the 
working face. It excludes the end use 
handling. Work activities in this func- 
tion are directly related to production. 
Some examples of work activities are 

Transporting rock-dust bags. 

Transporting roof bolts. 

Transporting timbers. 

3. Section move. This function re- 
lates to the handling of materials from 
the surface yard to the section being 
moved. It also includes the handling 
during the process of moving a mining 
section. Some examples of work activi- 
ties are 



Moving haulage belts. 



Replenishing transformer oil, 
hydraulic oil. 



5. Mine maintenance. 



This function 



relates to handling of materials from the 
surface yard to the point of end use 
for mine maintenance. It also includes 
final handling during scheduled and 
unscheduled mine maintenance. Mine main- 
tenance activities include the mainte- 
nance of roof, floor, ventilation, path- 
ways, rail track, and the like. It 
excludes equipment maintenance activi- 
ties, but includes those activities on 
equipment which form part of the mine 
installation. Some examples of work 
activities are 

Erecting stoppings for 
ventilation. 

Setting props and crossbars for 
roof support. 



Tearing up and re-laying rails. 

Transporting cables. 

Moving air lines, compressors. 

Longwall face supports. 

4. Equipment maintenance . This func- 
tion relates to the handling of materials 
from the surface yard to the point of 
use. It also includes final handling ac- 
tivities during maintenance of mine 
equipment. Some examples of work activi- 
ties are 

Extracting motors from continuous 
miners. 

Replacing of extinguisher 
canisters. 



Laying rail. 

Upgrading track. 

Table 1 gives examples of materials 
associated with various handling func- 
tions for further understanding of the 
work activities associated with each 
function. Each of the handling functions 
can be categorized by the type of ma- 
terials handled, the usage frequency, 
and the flow path. The flow path indi- 
cates the path followed by the materi- 
als in reaching the end use. The flow 
paths and the typical materials moved in 
each of the handling functions are de- 
scribed in appendix A. The handling 
functions will be used later to analyze 
the accidents associated with materials 
handling. 



TABLE 1. - Examples of materials handled in various handling functions l 

Materials handled Handling functions ^ 

Roof and rib support items: Roof bolts, roof Production end use, production supply 
bolt plates, expansion heads, half headers, 
timbers, steel beams, hydraulic jacks, crib 
materials, cement, sand. 

Fire protection items: Rock dust, extin- 
guisher cannister, foam tank. 



mine maintenance. 



All handling functions. 



Coal handling equipment items: 

Belting, jacks, conveyor parts, rollers. Production end use, production sup- 
stands. ply> equipment maintenance, section 

move. 
Shuttle cars, face equipment Equipment maintenance, section move. 



Vehicle maintenance items: Tires, cans of 
hydraulic oil, grease, and brake fluid, 
motors, handtools and power tools, welding 
equipment. 

Air supply items: Air lines, compressors, 
hoses, line fittings. 

Water supply items: Hoses, pipes, pumps, 
line fittings. 



Production supply, equipment 
maintenance. 



All handling functions. 



Production end use, production sup- 
ply, section move, mine maintenance. 



Ventilation items: Tubing, brattice, motors, All handling functions, 
brackets, hardware. 



Power supply items: Wire and cable spools, 
motors, transformers, cans of transformer 
oil, J hooks, motors, meters, power units, 
trailing units, trailing cables and con- 
nectors, breaker and switching panels. 



Do. 



Personnel support items: Food and water Production end use, production sup- 
containers, toilets, first aid kits, ply» section move. 

handtools. 

'Based on classifications in a study of 27 mines reported in the second work of 
footnote 3. 

^The end use handling associated with section move, mine maintenance, and equipment 
maintenance is included in the respective functions. End use handling associated 
with production handling function is classified as a separate function. 



CURRENT PRACTICES IN MATERIALS HANDLING OPERATIONS 



Many methods exist for handling materi- 
als among underground coal mines. More- 
over, different methods may be used for 
different materials within the same mine. 
Each mine, however, seems to have an es- 
tablished set of procedures for handling 
production, mine maintenance and equip- 
ment maintenance materials, and for ad- 
vancing or retreating a section. 

HANDLING OF PRODUCTION AND MINE 
MAINTENANCE SUPPLIES 

In terms of tasks and worker activi- 
ties, production supply and mine mainte- 
nance are closely related. For this rea- 
son the discussion of these functions has 
been combined. 

Production and mine maintenance materi- 
als are nearly always handled by a set of 
routine procedures. A typical cycle of 
events in this materials handling process 
could include the following: 

Transferring materials from commercial 
carriers to a surface storage area, and 
loading them on supply trips in their ex- 
isting packaged form to be transported to 
the section. 

Breaking the bindings of materials in 
packaged form and transferring individual 
items or small bundles of items from the 
supply trip to the section storage area. 

Transferring the materials from the 
section storage area to an area near the 
working face. 

Transporting the individual items for 
their end use. 



received roof bolts in packages of 10 
with a number of packages strapped to a 
pallet. 

Forklifts, cherrypickers, front-end 
loaders, and cranes are sometimes used to 
help unload and stack the materials in 
the surface storage area, but all mines 
studied used some degree of manual hand- 
ling at the surface. Some materials are 
loaded in their packaged form, though it 
is more common to have individual items 
or small bundles loaded manually into the 
vehicle for the trip into the mine. Some 
mines perform bulk handling of rock dust 
and oil. In these cases, the surface 
yard will have bulk storage facilities 
for these items after they have been re- 
ceived from the supplier. Rock dust may 
be pneumatically transferred into a rock- 
dust bin from a truck or railroad car. 
Hydraulic oil is pumped into a bulk tank, 
or the mine may have an "oil house" where 
it cleans, empties, and fills containers 
to be transported to the section. 

Typically, section supervisors will 
generate lists of their supply needs. A 
surface crew will take the list from each 
section and assemble a supply trip. In 
some mines, the supply function is a 
scheduled effort that tries to anticipate 
production and mine maintenance needs 
rather than responding to demand. The 
supply trip will deliver a scheduled 
amount of supplies in accordance to the 
linear advance expected from the section. 
In large mines , it is common for the sup- 
ply trips to be loaded on the first shift 
and hauled into the mine on the third. 
The supply logistics are less formal for 
the smaller mines of one or two sections. 



A general discussion of production 
and mine maintenance handling methods 
follows. 

Handling on the Surface 

Materials usually arrive at the mine 
by truck or railroad. Most often they 
are packaged on pallets or in strapped 
bundles. It was noted that some mines 



Transport to the Section 

The methods of transporting supplies to 
the section change with the items to be 
handled. Solid supplies, such as roof 
bolts, posts, blocks, and crossbars, are 
transported as individual items or pal- 
lets by means of mine cars or rubber- 
tired vehicles. Large volume liquid and 
granular supplies, such as rock dust. 



hydraulic oil, and water, are put into 
containers and transported on vehicles or 
handled in bulk. form. 

There are several types of solid items 
with different weights and sizes involved 
in the production and mine maintenance 
supply function. Table 2 outlines a typ- 
ical list of items and average use per 
day per section. 



battery-powered vehicles, scoops, and/or 
tractor-trailer combinations. 

2. Rail haulage with a track laid in a 
section heading as far as the tailpiece 
using railcars pulled by a motor. 

3. Rail haulage with track not extend- 
ed into the section and transferring di- 
rectly to battery-powered vehicles. 



TABLE 2. - Description and usage 
of typical supply items 



Supply 


Weight, 


Av. 




lb 


use 


2- to 12-foot plates, roof 






bolts , and shells .......... 


4- 12 
50 


123 


Rock dust sacks............. 


75 


2- by 6-in to 6- by 8-in, 1- 




to 16-ft lengths of timber. 






boards, and headers 


8-270 


61 


16- by 8- by 4- or 6-in 






8 topping blocks 


27- 65 


52 


8- to 13-ft header steel.... 


10- 16 


25 


Bit: 






Continuous miner. ......... 


<1 
<1 

40 


18 


Roof drill 


16 


5— gal oil container. ........ 


1 5 


4- to 10-in diam, 3- to 15- 




ft round timber posts 


34-320 


15 


1- to 6-ft crib block 


20- 60 


12 


Mortar mix sacks. ........... 


90 
60 


3 


75-ft brattice roll 


<1 



'Based on yearly supply 
2 7 mines reported in the 
footnote 3. 



consumption of 
second work of 



A major difference in transport to the 
section involves the use of area storage. 
A few mines use intermediate storage lo- 
cations, each of which serves several 
working sections. This method requires a 
transfer from the supply trip to stacks, 
usually along the rib of the supply en- 
try, and then another transfer to a vehi- 
cle for haulage into the section. 

Most mines transport directly from sur- 
face storage to the section without an 
intermediate storage area. There are 

four methods of transport in conmion use 



4. Rail haulage with track not extend- 
ed to the section using rubber-tired or 
railcars until the end of the track and 
then converting to rubber-tired haulage 
by battery-powered tractors. 

5. Another method, though not in com- 
mon use, is to reverse the conveyor belt 
to handle materials; this requires manual 
handling at the loading and unloading 
point. 

Many methods exist for handling bulk 
materials, such as rock dust and hydraul- 
ic oil. In the case of rock dust, the 
need to handle bagged rock dust has been 
practically eliminated by the use of one 
of the following bulk transportation 
methods: 

1. Rock dust is pneumatically piped 
into a rock-dust car at the section. In 
smaller mines, it is piped directly to 
the face. 

2. Rock dust is fed by gravity through 
a borehole or through a casing suspended 
from an air shaft into a rock dust car 
and then hauled to the section. 

3. Rock dust is unloaded from a bin 
into a rock dust car at the surface. 

Two methods of handling bulk oil in- 
clude having it flow by gravity from an 
oil tank at the surface into an inter- 
mediate storage area, or using 55-gal 
drums transported by supply vehicle to 
the section. 

Handling in the Section 



1. Rubber-tired haulage in drift mines 
where the distance from surface to 
section is short (less than 1 mile) using 



Once the railcar or other supply vehi- 
cle has arrived in the section two or 
three crosscuts from the working face. 



items are usually unloaded and stacked. 
In some mines, the vehicles are parked at 
the section and the materials are used 
directly. 

If the supply vehicle is left in the 
section, there is less handling of mate- 
rials; however, mines vary in their will- 
ingness to leave cars in the section for 
two reasons. First, leaving the car 
takes up room and makes switching diffi- 
cult, and second, more supply cars are 
required. 

Haulage of supplies from section stor- 
age to end use is accomplished several 
ways 

Manual carrying. 



be found in section storage locations. 
These locations vary from a small under- 
ground shop with an overhead hoist to 
storage stacks in a crosscut along a sup- 
ply route. Some frequently used items 
such as shuttle car wheels and hydraulic 
hoses, can often be found in section 
storage. 

When a machine component is needed, it 
is generally transported by the quickest 
means possible to minimize downtime. 
Problems are frequently encountered owing 
to the weight of the item (sometimes over 
2,000 lb). These materials are usually 
handled with a combination of manual 
handling and mechanical devices such as 
a machine-mounted winch, come-along, or 
jack. 



Battery-powered vehicles such as 
scoops, tractors, and personal 
carriers. 

Face equipment, such as roof bolters, 
shuttle cars, and rock dusts. 

When oil is transported in bulk to the 
section, the usual procedure is to fill 
5-gal containers and carry them to final 
use. 

HANDLING OF EQUIPMENT 
MAINTENANCE MATERIALS 

The handling of equipment maintenance 
materials usually follows very undefined 
paths. Some components are kept in sur- 
face storage, but more likely they will 



HANDLING OF SECTION MOVE SUPPLIES 

The advance of the section calls for 
the addition of conveyor sections, elec- 
trical cable, and track, plus the trans- 
port of equipment, such as a tailpiece, 
belt feeder, or power boxes. While these 
materials usually follow the conventional 
supply route, their size and weight re- 
quire special handling. This is accom- 
plished using a combination of manual 
handling and powered equipment. 

For longwall sections, specially de- 
signed lift-transporting devices have 
been developed to handle roof supports 
which present a problem owing to their 
weight (10,000-lb range) and distances 
they must be moved. 



MINE ENVIRONMENT AND MATERIALS HANDLING METHODS 



There are many environmental factors 
that have an effect on a mine materials 
handling method. These include 

Mine size. 

Portal; drift, slope, shaft. 

Mining method; continuous, conven- 
tional, longwall. 

Coal haulage; belt, rail. 



Seam height. 

Stage of development; advance, 
retreat, rooms. 

The size of the mine plays a role in 
determining the equipment available for 
materials handling. Some mines are small 
enough to use battery-powered scoops or 
tractors to haul materials from the sur- 
face to the section. Large mines are 
more likely to use forklifts and cranes 



for surface handling because they have 
higher utilization of such equipment. 

The type of portal effects the diffi- 
culty of transporting the materials into 
and out of the mine. Transportation into 
a drift mine is usually the easiest since 
a locomotive can often run in and out of 
the mine. At slope mines, it is common 
practice to lower the supply trip into 
the mine using a hoist. The shaft mine 
poses the most problems since a train of 
cars cannot be transported into the mine. 
In some cases, they can be lowered one 
car at a time by hoist; or where cars 
cannot be hoisted, materials must be 
doubly handled. 

The mining method has the largest ef- 
fect on the types of materials that are 
handled. Conventional mining involves 
essentially the same materials handling 
methods as continuous mining except for 
the special requirements for handling ex- 
plosives. However, longwall mining has 
radically different requirements. Mate- 
rials, such as roof bolts, rock dust, and 
stopping blocks, are used only on a lim- 
ited basis for development. The descrip- 
tion for handling equipment maintenance 
materials and section move could serve as 
the general pattern for longwall sec- 
tions, except that in longwall mining the 
section move is a massive operation. 

The method of coal haulage does not 
appear to have a large impact on handling 
methods because track is generally laid 



for personnel and supply movement even in 
mines with belt haulage. Probably the 
largest factor influencing the movement 
of materials is the scheduling problems 
encountered between supply trips and coal 
haulage on the main line track 

Seam height has a large impact from 
several aspects. A high-seam mine opera- 
tion is better able to lay track up to a 
section because it is not faced with the 
costs of cutting roof or bottom to pro- 
vide height clearance. In low mines, 
problems are encountered when loading 
supplies in and out of supply cars be- 
cause of limited clearance between the 
sides of the car and the roof. This same 
problem makes it impossible to use avail- 
able overhead lifting devices. Another 
problem results because manual lifting 
and carrying must be done while bending 
over, which is extremely strenuous to the 
back. 

The stage of mine development has an 
impact mainly on the materials used. 
Material usage changes significantly 
between advance and retreat mining. For 
instance, in retreat mining, more timber 
is used and new stoppings will not be 
erected. The major problem with retreat 
mining is associated with recovery of 
materials. As the section retreats, 
materials such as conveyor sections, 
track, water pipe and electrical cable, 
must be pulled out of the section and 
stored. 



PROBLEM AREAS IN THE PRESENT MATERIALS HANDLING SYSTEMS 
IN UNDERGROUND COAL MINES 



Interviews with mine operators and 
equipment manufacturers have indicated a 
general awareness of materials handling 
problem areas such as accidents, supply 
function, labor costs, and production de- 
lays due to maintenance and production 
supply system breakdowns. 6 The produc- 
tion materials handling function supports 
most other activities in the mine and is 
affected by its interaction with other 
operations. Daily supply items such as 
roof bolts, timber bolts, and concrete 

"First work cited in footnote 3. 



blocks, are needed at various locations 
at different times. The movement of mine 
maintenance and equipment maintenance 
materials, such as replacement motors, 
are vital to keeping production going. 
Section move, though not as common an oc- 
currence, poses special hazards owing to 
the size and weight of the items being 
handled. 

Meeting these needs requires the 
movement and handling of materials by 
most mine personnel. Their activities 
are based on the quantities of items 



10 



required, times when they are needed, 
physical characteristics of the items, 
transfers between transport equipment and 
storage, availability of transport and 
other handling equipment, communications 
systems among the supply personnel, in- 
formation exchange between the supply 
personnel and other miners, and the pre- 
dictability of supply needs at various 
locations underground. The following 
sections discuss problems related to the 
above factors. 

PERFORMANCE OF HAZARDOUS 
MANUAL ACTIONS 

Manual handling of items is very common 
in underground coal mines. Typically, 
materials are loaded and unloaded from 
vehicles, placed in storage, carried, or 
simply held unsupported. Such manual 
handling occurs in support of mine opera- 
tions such as production, mine mainte- 
nance, equipment maintenance, and section 
move. Manual actions directly associ- 
ated with accidents can be grouped as 
follows: 

Stationary actions (transfer) 

Lifting or lowering without support 
(supply item is supported manually). 

Pushing or pulling with support (sup- 
ply item is on floor or surface of a 
vehicle) . 

Holding without support (supply item 
is held manually). 

Walking actions (transport) 

Carrying without support (supply item 
is held manually). 

Pushing or pulling with support (sup- 
ply item is on floor, skid, or on surface 
of a vehicle). 

End use actions 

All actions connected with the final 
application of supply items and not sep- 
arately classified as stationary or walk- 
ing actions. 



ACCIDENT ANALYSIS OF HANDLING 
FUNCTIONS AND ACTIONS 

Accident data used were obtained in 
a study of 27 mines representative of 
the coal mining industry profile. 7 These 
data were taken from mine accident rec- 
ords for 1973. 

In the 27 mines sampled, a total of 269 
materials handling accidents took place. 
A total of 771 days were lost because of 
these accidents. The total hours worked 
were 10.356 million and total coal pro- 
duction was 15.121 million tons. Acci- 
dent data were analyzed for the handling 
functions and actions defined earlier. 
Accident frequencies, days lost, and 
severity were calculated for various 
handling functions and actions and are 
presented in appendix B.8 The following 
paragraphs highlight the findings of this 
analysis. 

The reported accident data were ana- 
lyzed for frequency and severity with 
reference to manual actions and han- 
dling functions. The following signifi- 
cant observations resulted from the 
analysis: 

The production supply and mine mainte- 
nance functions are highly hazardous sup- 
ply environments. 



They account for 
accidents. 



60% 



of the 



They account for 76% of the days 
lost. 

Accident severity (6.26) is the high- 
est in the mine maintenance function. 

Accident severity (3.25) is also high 
in the production supply function. 

Stationary manual actions in the pro- 
duction supply and mine maintenance func- 
tions are the largest contributors to the 
total accidents. 



8 



Second work cited in footnote 3. 

See appendix B for definitions of fre- 



quency, days lost, and severity. 



11 



Lifting and lowering without support is 
a highly hazardous manual action in ma- 
terials handling. It accounts for 59% of 
all accidents and 54% of days lost. 

Manual carrying without support is a 
hazardous action with high accident se- 
verity (4.11). 

INEFFICIENT UTILIZATION 
OF SUPPLY LABOR 

In general, supply-related personnel 
are underutilized in that their produc- 
tive time is less than half of the work- 
ing shift. Considerable time is spent in 
traveling to and from work, areas, wait- 
ing, returning empties, and the like. In 
some mines, a large fraction of the time 
is lost owing to early quitting, late 
starting, and traffic conflicts. Some 
identifiable factors related to this 
problem include 

Performance standards have not been 
developed, therefore, staffing and sched- 
uling or performance control is based al- 
most entirely on experience and guess- 
work. 

Staffing of the supply function is 
based on past history, experience, and 
anticipation of peak loads, which results 
in overstaf f ing. 

For some items the usage quantity, 
place, and time are predetermined. Yet a 
large number enter the mine on an as- and 
when-needed basis. The lag time between 
a supply requisition by the section or 
mine supervisor from the surface yard and 
the actual delivery of the item encour- 
ages the supervisor to overstock supplies 
in advance. Very few supply scheduling 
plans exist. 

In general, predetermined routing of 
items to the working section does not ex- 
ist and is rarely followed when it does. 
This creates hazards and makes supervi- 
sion difficult. 

Communications between personnel han- 
dling material is difficult because of 
noise and poor visibility. 



Good information exchange between the 
section and mine supervisor and the sup- 
ply crew do not normally exist. 

PERSONNEL PROBLEMS 

Several personnel problems were iden- 
tified as reducing the efficiency of 
materials handling operations, as well as 
increasing the possibility of an injury 
in the performance of manual handling 
tasks. 

Job bidding in union mines gives the 
workers an opportunity for higher wages 
and job advancement. This generally re- 
sults in junior, more inexperienced per- 
sonnel staffing the supply function or 
doing other manual labor. 

Stretching physical limits and capabil- 
ities in manual handling of materials 
often result in injuries to personnel 
with inadequate physical capability in an 
effort to meet job requirements. 

Very little formal safety training is 
obtained by supply personnel because most 
of the training is "on the job." Also, 
there is little training given on tech- 
niques for manual handling of materials 
in an underground environment. 

WEIGHT OF SUPPLY ITEMS 

Table 2 outlines the size and weight 
ranges and average daily section usage of 
some common supply items. Many supply 
items such as rails, timber, headers, 
stopping blocks, crib blocks, bags of 
rock dust or mortar mix, and the like, 
are of considerable weight. The manual 
handling of such supply items in a low 
roof, poor footing environment increases 
the probability of accidents and handling 
time, even though they are usually 
handled by more than one person per item. 
In general, very few attempts have been 
made at weight reduction of supply items. 
A known exception is the recent use of 
fiberglass beams by some mines. These 
beams are considerably lighter than 
timber. 



12 



Figures B-5 and B-6 of appendix B give 
frequencies and severities for accidents 
occurring while handling supply items of 
various weight groups. The accident data 
indicate the following: 

Most of the accidents occur while han- 
dling supply items in the 1- to 100-lb 
weight group. 

Typical supply items in this weight 
group are roof bolts, short timber, 5-gal 
oil containers, rock dust or mortar mix 
bags, belts, and stopping block. 

The 1- to 100-lb weight group accounts 
for the majority of days lost. 

Accident severity is very high for 
the 200- to 500-lb weight groups taken 
together. 

Typical supply items in this weight 
group are electric motors, equipment com- 
ponents, haulage rails, PVC and steel 
pipes, pumps, timber, and large oil 
drums. 



HAZARDOUS ENVIRONMENTAL CONDITIONS 

The underground mine environment is 
considerably more hazardous and difficult 
to work in as coii^)ared to most surface 
environments. Such conditions not only 
increase the probabilities of accidents, 
but also reduce the rate of manual work. 
Some examples of hazardous handling oper- 
ations due to the environment are as 
follows: 

Bending or Sitting on folded legs is 
common in mlp.es of low roof height. 
Holding without support, lifting, or car- 
rying weight under such conditions can 
result in back injuries. This cumbersome 
position causes worker fatigue and 
increases the potential for dropping 
loads. 

Poor maintenance of the mine bottom re- 
sults in slippery and uneven footing. 
Manual handling actions performed under 
such conditions increase the potential 
for accidents. 



SUMMARY 



Materials handling accidents have been 
identified as a significant problem area 
in underground coal mines. Bureau of 
Mines research has provided a better un- 
derstanding of the numerous factors con- 
tributing to materials handling problems. 

In this paper, descriptions and exam- 
ples of current materials handling meth- 
ods and problems in underground coal 
mines have been presented, as reported in 
Bureau of Mines research studies. Mate- 
rials handling activities have been de- 
fined by the various mining operations 
which describe their general purpose. 
These materials handling functions are: 
Production End Use, Production Supply, 
Section Move, Equipment Maintenance, and 
Mine Maintenance. 



A survey of a representative sample of 
underground coal mines^ has resulted in 
a description of the methods, practices, 
flow paths, and items typical of materi- 
als handling activities. In addition, 
several specific problem areas associ- 
ated with materials handling in under- 
ground coal mines , such as manual hand- 
ling actions accidents, inefficient use 
of labor, and hazardous environmental 
conditions, have been discussed. In sum- 
mary, this paper has provided an over- 
view of the methods and problems of ma- 
terials handling in underground coal 
mines. 



^Second work cited in footnote 3. 



13 



APPENDIX A.— FLOW PATHS AND MATERIALS FOR VARIOUS MATERIALS HANDLING FUNCTIONS 

Figures A-1 through A-5 illustrate flow each figure. The flow paths also show 

paths of materials in various operating locations at which manual transfer, 

environments defined by the handling transport, and end use actions are per- 

f unctions. Only the major items of the formed on the materials, 
handling function have been listed in 



14 



APPENDIX B. —ACCIDENT ANALYSIS 



Accident data collected in a study of 
27 mines has been analyzed in this ap- 
pendix. Accident frequencies, severity, 
and days lost have been calculated for 
various handling functions, manual haz- 
ardous actions, and weight groups of 
items. Figures B-1 through B-6 illus- 
trate the results of these analyses. In 
the following sections, accidents are 
further discussed in terms of various 
handling functions. Some definitions 
used in these discussions include: 

Frequency — The number of accidents for 
a particular handling function. 

Severity — Frequency divided by the num- 
ber of days lost for a particular hand- 
ling function. 

Days lost — Actual days lost from work. 

PRODUCTION SUPPLY AND MINE 
MAINTENANCE FUNCTIONS 



of the accidents in this handling func- 
tion. (Refer to table B-1.) 

Stationary actions account for 77% of 
the accidents in this function, while 
walking actions relate to 23%. 

Cable handling poses a handling problem 
different from the other materials used 
in this function. At intersections, the 
cable has to be lifted and hung from a 
hook anchored to a roof bolt. It also 
has to be pulled in advance of tramming 
equipment to prevent damage by tramming 
over the cable. The production end use 
function accounts for 30% (out of 269) 
accidents, but only 5% of the total 771 
days lost. The accident severity is con- 
siderably lower than other functions, 
1.17 days lost per accident, 

TABLE B-1. - Number of accidents 
classified by manual actions in 
the production end use function 



Since most of the materials used and 
manual actions are similar for these 
functions and since their activities are 
closely related, the accident data for 
these two functions have been combined. 

Sixty percent (160 out of 269) of all 
manual handling accidents take place in 
the production supply and mine mainte- 
nance functions. The number of days lost 
owing to accidents in these two functions 
together account for 76% (588 out of 771 
days lost). The severity of accidents in 
the mine maintenance function is the 
highest, 6.26 days lost per accident. 
The severity in the production supply 
function is also high, 3.15 days lost per 
accident. 





Weight, 
lb 


Accidents 


Item 


Sta- 


Walk- 






tionary 


ing 


6- by 6-in by 5- 








to 8-ft (closed) 








roof jack 


50- 70 


3 


4 


6- by 8-in by 10- 








to 14-ft crossbar 


160-225 


5 





6-in-diam by 5- to 








8-ft round posts. 


48- 76 


3 


2 


2- to 3-in-diam 








trailing cable... 


15- 10 


4 





Other items 


NAp 


8 


1 


Total 


NAp 


23 


7 



NAp Not applicable. 
1Per foot. 



SECTION MOVE FUNCTION 



Most of the accidents in these func- 
tions are related to stationary actions 
(38% of 269). Walking actions account 
for the next largest number of accidents 
in these functions (18% of 269). 

PRODUCTION END USE FUNCTION 

Roof jacks, crossbars, round posts, and 
trailing cables account for the majority 



A major move of a production unit from 
one section to another is infrequent, oc- 
curring from one to three times per year. 
Most of the handling actions and materi- 
als are similar to other functions. A 
number of manual handling actions are in- 
volved during the section move operation. 
Handling of rail, belt, and belt rollers 
cause the majority of accidents in this 
function (table B-2). In some mines. 



15 



TABLE B-2. - Number of accidents classified by manual actions for some materials 
in the section move function 



Item 


Common usage 


Weight, 
lb 


Accidents 




Stationary 


Walking 


40- to 85-lb rail, 20- to 39- 

ft length. 
Belt roller, 4-in-diam by 36- 

in length to 6-in-diam by 

42-in length. 
Belt, 36- and 42-in width.... 
Rail tie, 8 by 6 by 72 in.... 
Belt chain, 8 by 9 by 52 in. . 


Coal, supply haulage.. 
Return (bottom) idler. 

Coal haulage 

Support for rail 

Carrying (top) idler.. 


266-1,100 
40- 50 

NA 
90- 100 
20- 25 


9 

4 

4 
1 

1 


6 
1 


1 




Total 


NAp 


NAp 


19 


8 



NA Not available. NAp Not applicable. 



rails are manually rolled off a supply 
car and then manually dragged into place, 
which is a hazardous practice. In other 
mines, the rail is attached by a chain to 
a scoop, battery tractor, or the like, 
and is pulled out of the supply car and 
then pulled into place by the transport 
vehicle. This handling practice, too, is 
considered hazardous. 

Section move accounts for 13% (out of 
269) accidents, with 7% (out of 771) days 
lost. 

EQUIPMENT MAINTENANCE FUNCTION 

This function accounts for the next 
largest number of accidents, 16% (out of 
269) and days lost, 12% (out of 771), as 
compared with production supply and mine 
maintenance functions. Stationary ac- 
tions performed during removal and re- 
placement of heavy equipment parts, such 
as motors, rubber tires on haulage vehi- 
cles, and the like, account for most of 
the accidents in this function. 

Most of the items in this function are 
in the 50- to 200-lb range and are usu- 
ally handled by one to four miners. 



Another major source of accidents is the 
manual handling of 5-gal cans of hydraul- 
ic oil, tool boxes, and welding gas bot- 
tles. Generally, tool boxes weigh up to 
100 lb and require two miners to lift or 
carry them. 

Table B-3 gives the accident frequen- 
cies for various materials and hazardous 
manual actions for the equipment mainte- 
nance function. 

TABLE B-3. - Number of accidents classi- 
fied by manual actions for some mate- 
rials in the equipment maintenance 
function 





Accidents 




Sta- 
tionary 


Walk- 
ing 


Face equipment components. 

Repair supplies (oil cans, 
wire reels, etc.) 

Repair supplies (tool- 
boxes, gas bottles 

Shuttle car components.... 

Other equipment components 

Belt conveyor components.. 


7 

5 

5 
7 
7 
4 


2 

4 

3 





Total. 


35 


9 



16 



Surface 
storage 







Belt 
Belt entry move up 



KX 



Track entry 



Track move up 



Area 
storage Section storage 



DOO 



Production working place 





KEY 

D 

Manual 
transfer 

O 

Manual 
transport 

O 

End use 
handling 



Major materials ranked by usage frequency 
•Roof bolts, plates, and shells . Bits -continuous miner 

• Wedges . Bits- roof drill 

• Rock dust sacks • Timber- round posts 

• Timber- boards and headers . Crib block 

• Header, steel . Brattice cloth 

FIGURE A-l. - Production supply function flow path with materials used. 



17 



Surface 
storage 




Belt 
Belt entry move up 



K>0 



Track entry 



Track move up 



Area 



DO-O 



storage Section storage Production working place 



DtCIOOO 



o 




Equipment 
maintenance 



J^ 



KEY 

D 

Manual 
transfer 

o 

Manual 
transport 

O 

End use 
handling 



Major materials ranked by usage frequency 



• Wedges 

• Rock dust sack 

• Timber - boards and headers 

• Stopping blocks 



• Timber-round posts 
•Crib block 

• Mortar mix sack 

• Pipe-PVC and steel 



FIGURE A-2. - Mine maintenance function flow path with materials used. 



18 



Belt 
Belt entry move up 



Surface 
storage 



o 



KH 



Track entry 



Track move up 



Area 
storage Section storage 




Production working place 



KXTD 



O 




Equipment 
maintenance 



KEY 

D 

Manual 
transfer 

o 

Manual 
transport 

O 

End use 
handling 



Major materials ranked by usage frequency 

• Roof jack, portable 

• Trailing cable 

• Wire 

FIGURE A-3. - Production end use function flow path with materials used. 



19 



Surface 
storage 




Belt 
Belt entry move up 



hO< 



Track entry 



"-"''^-^'"'^' 



Track move up 




Area 
storage Section storage Production working place 



brK>^3 





Equipment 
maintenance 






fS^Jf^^lw^^ 



Xh-'X^ii&fi'.-.-i 



KEY 

D 

Manual 
transfer 

O 

Manual 
transport 

O 

End use 
handling 



Major materials ranked by usage frequency 

• Lubricant containers 

• Equipment components 

• Bottles, welding gas 

• Tool boxes 

FIGURE A-4. - Equipment maintenance function flow path with materials used. 



20 



Surface 
storage 



JJW^V*-'!.-:'^;'.' 



?A;-?-..''r ^'i'via 




Belt 
Belt entry move up 



Area 




storage Section storage Production working place 




Equipment 
maintenance 



KEY 

D 

Manual 
transfer 

o 

Manual 
transport 

O 

End use 
handling 



Major materials ranked by usage frequency 
•Conveyor belt 'Belt support stand 

• Carrying idlers • Haulage roil 

• Return idler 'Timber 

FIGURE A-5. - Section move function flow path with materials used. 



21 



140 
130 
120 
110 
100 

CO 

z 90 

UJ 

o 

o 80 

(J 

< 

li. 70 



133 (50%) 



Total number of accidents = 269 



44 { 16%) 



27(10%) 



30(11%) 



n 



35 (13%)- 






i>-? 
X-> 
^^V 






FIGURE B-1, - Accident frequencies for different 
handling functions. 



6.^6 


(169) 




7 






t 


KEY 




Totol number of accidents ■ 269 




Total average seventy- 2.87 




Total days lost "771 


- 


Figures in ( ) ore days lost 




/ 






/ 




_ 


/ 


_ 


J./ 5 


^ 




(419) 






' 




s 




- 






2.07 

(91) 

7\ 

1.17 / 

(35) ^ . 

71 ^ 


1.63 
(57 

1 






^ 






/ 




/ 












^ 




/ 




/ 






/ 




/ 






/ 




/ 











6</ 






^.^ 



FIGURE B-2, - Accident severity for various han- 
dl ing functions. 



180 

ISO 

I 40 

120 

100 

80 

60 

40 

20 



:p^ 



Lifting or lowering 

without support 

158 (59%) 



\X>th 



Total nunnber of accidents = 269 



Carrying 

without support 

56(21%) 



Holding 

without support 

1 1 (4%) 



Pushing or 
pulling 
with support 
9 (3%) 



Stationary 
( transfer) 
178 (66%) 



A 



Pushing or pulling 

with support 

17 (6%) 

End use action 
in all modes 
18 (7%) I 



A. 



Walking 
(transport) 
73 (27%) 



All end use 
18 (7%) 



FIGURE B-3. - Accident frequencies for differ- 
ent hazardous manual actions. 




Stationary 

(transfer) 

(484) 2.61 



Walking 
(transport) 
(264) 3.62 



All end use 
(43) 2.39 



FIGURE B-4, - Accident severity for various man- 
ual hazardous actions. 



22 






q: 
lij 
> 

LiJ 



LU 
O 

O 
O 
< 



5.4 

(156) 

F 



S.2 

(273) 

F 



(256) 



.es 

(17) 



/I M 



KEY 
Total days lost = 771 
Total accidents=269 
Severity = 2.9 days lost 
per accident 
Figures in ( ) = total doys 
lost 



3.4 

(41) 

17 



2.6 

(21) 



A 



.A 



.68 

(7) 
F 



(0) (0) 



^.^-/^o%o^o%o%^o o- o- 



MATERIAL WEIGHT GROUPS, lb 

FIGURE B-5. - Accident frequencies for various 
manual handling accidents in materials weight 
groups. 





1 10 




100 




90 




80 


Z 




liJ 

a 


70 


() 




o 


ttO 


< 




u. 
o 


50 


tr 




LJ 


40 


m 





- 86 
F 



30 
20 
10 



97 



The weight group is only an 

indication of the physical 

characteristics of the materials. 

It should not be confused with the 

desirable load capacity of any 

potential equipment. 



20 



12 



\V\\A^,^\7\ 



^ r> C^ o>' r>' o> ^\' 



v°^ ^°^ >,Q^ 



^Q ^ 



^ ^^ 



MATERIAL WEIGHT GROUPS, lb 

FIGURE B-6. - Accident severity for manual han- 
dling accidents in various materials weight groups. 



23 



ACTIVITIES AND OBJECTS MOST COMMONLY ASSOCIATED WITH UNDERGROUND 
COAL MINERS' BACK INJURIES 

By Robert H. Peters 1 



ABSTRACT 



Recent national statistics on factors 
associated with underground coal miners' 
back injuries are presented. Particular 
attention is given to describing combin- 
ations of events and conditions that 
account for over 1 pet of these back, in- 
juries. Most of the statistics present- 
ed in this paper are derived from Mine 



Safety and Health Administration's (MSHA) 
records of injury data and short narra- 
tive accounts of injuries. It is con- 
cluded that since there are such a vari- 
ety of factors that contribute to back 
injuries, significant improvements can 
be realized only through a broad, multi- 
faceted approach to prevention. 



INTRODUCTION 



There is reason to believe that the en- 
vironmental conditions that exist in many 
underground coal mines pose relatively 
unique barriers to the prevention of back 
injuries. Compared with most other types 
of industrial settings, many underground 
coal mines are not as well illuminated, 
are wetter, and have more restricted work 
spaces. The problems of illumination and 
water can result in back injuries caused 
by slipping on wet or muddy surfaces or 
tripping over things that could not be 
seen clearly. Coal seams that prevent 
miners from standing erect contribute to 
the occurrence of back injuries because 
miners who must stand, walk, lift, and 
carry things in a stooped position place 
significantly more stress on their backs 
than those who can perform these activi- 
ties while standing erect. 

Back injuries are unquestionably the 
most common type of injury suffered by 
miners. A few statistics based on injury 
data reported to MSHA help to portray the 
significance of the problem. 

Table 1 presents the total reported in- 
juries and overall incidence rates and 
severity measures associated with back 
injuries suffered by U.S. coal miners 
while working underground for each year 

^Research psychologist, Pittsburgh Re- 
search Center, Bureau of Mines, Pitts- 
burgh, PA. 



from 1978 to 1981. No trends are appar- 
ent in the figures for total injuries and 
incidence rates. The total number of re- 
ported back injuries over this 4-yr peri- 
od range from 2,654 to 3,779, and do not 
appear to be declining. The overall in- 
cidence rates over this 4-yr period range 
from 2.74 to 3.39, and also do not appear 
to be declining. The overall severity 
rates over this 4-yr period range from 
102 to 141, and definitely portray a 
trend of increasing severity. 

It should be noted that not all back 
injuries (especially the "minor" ones) 
are reported to MSHA. Therefore, it is 
very likely that, in reality, the numbers 
and incidence rates associated with back 
injuries are higher than those portrayed 
in table 1. 

TABLE 1. - Number, incidence rate, and 
severity of back injuries suffered by 
coal miners while working underground 



Year 


Number 


Incidence 
rate ' 


Severity^ 


1978 

1979 

1980 

1981 


2,654 
3,617 
3,779 
3,007 


2.74 
3.14 
3.39 
3.00 


102 
114 
136 
141 



'incidence rate is the number of back 
injuries per 200,000 worker-hours. 

^Severity is the number of lost work- 
days per 200,000 worker-hours. 



24 



Table 2 breaks down the total number of 
accidents that occurred inside under- 
ground coal mines during 1981 according 
to MSHA's categorization scheme for clas- 
sification of accidents. MSHA's accident 
classification scheme attempts to iden- 
tify the circumstances that contributed 
most directly to the resulting accident. 
The first column of numbers in table 2 
indicates that handling material accounts 
for a much greater percentage of total 
injuries than any other single class. As 
shown in the last column of table 2, in- 
juries to the back (as opposed to other 
parts of the body) account for almost 
half (42.7 pet) of the injuries associ- 
ated with handling material. Within 
classes containing relatively large num- 
bers of injuries, the back is generally 
associated with more injuries than any 
other part of the body. Altogether, back 



injuries account for 23 pet of all in- 
juries reported to have occurred inside 
underground coal mines during 1981. 

In terms of the number of workdays 
missed before the injured miner is able 
to return to work, back injuries are a 
relatively severe type of injury. 
Twenty-six percent of the lost-time back 
injuries that occurred inside underground 
coal mines during 1981 resulted in the 
miner missing more than 4 weeks of work. 
The average number of workdays missed 
after miners injured their backs was ap- 
proximately 7 days longer than the aver- 
age number for all nonfatal injuries (39 
versus 32 days). Altogether, 31 pet of 
all workdays lost to nonfatal work- 
related injuries were attributed to in- 
juries of the back. 



TABLE 2. - Injuries suffered by underground coal miners during 1981, 
broken down by accident classification and showing the percent 
of back injuries in each class 




Accident classification 



Percentage that 
are back injuries 



Electrical (current producing) 

Entrapment 

Exploding vessels under pressure 

Explosives and breaking agents 

Falling or sliding rock or material.. 

Fall of face or rib 

Fall of roof 

Fire 

Handling material 

Nonpowered hand tools 

Nonpowered haulage ' 

Powered haulage ' 

Hoisting' 

Explosion of gas or dust 

Inundation 

Machinery (includes power tools and 

mining machines )' 

Slip or fall of person 

Stepping or kneeling on object 

Striking or bumping^ 

Other 

Total and percentage 



1.6 






11.5 
12.9 

3.9 

3.2 
42.7 
10.8 
31.0 
16.3 

6.3 
.1 



7.6 
21.4 
10.5 
10.5 
28.7 



23.0 



'Accidents caused by the motion of the o 

^Excludes accidents that occurred while 

handtools, or operating and/or riding mach 



bject. 

handling material, using 
inery or haulage. 



25 



In total, these injuries represent only 
a tremendous economic cost to coal com- 
panies, to miners and their families, and 
to society; they represent a tremendous 
amount of human suffering. It is obvious 
that there is a great need to find better 
ways to prevent back injuries to under- 
ground coal miners. 

The success of those who search for 
better ways to prevent back injuries to 
underground coal miners is, in part, de- 
pendent upon the accuracy of their under- 
standing of the causes of back injuries. 
This paper attempts to add to what is 
currently known about the causes of back 
injuries to underground coal miners. The 



general approach employed was to review 
data from reports on an extensive number 
of back injuries recently suffered by un- 
derground coal miners, to identify the 
basic types of accidents causing these 
injuries, and to search for events and 
conditions that are commonly associated 
with them. The first section describes 
how the data were obtained, the types of 
injuries that were included, and the 
types of analyses that were performed. 
The second section presents the results 
of data analyses and a few speculations 
concerning how various types of accidents 
might be prevented. The third section 
summarizes the findings. 



THE SOURCE OF DATA AND METHODS OF ANALYSIS 



The types of injuries included in the 
statistics presented in the remainder of 
this paper are those in which a coal min- 
er suffered a ruptured disk or a strain 
or sprain of his or her back while work- 
ing at an underground location. The data 
are derived from reports that the opera- 
tors of U.S. coal mines sent to MSHA con- 
cerning injuries their employees suffered 
while at work during 1981. Employers are 
required by 30 CFR 50.2 to report to MSHA 
all injuries that cause an employee to 
miss one or more days of work. However, 
if the injury did not require the em- 
ployee to miss work, and meets certain 
other conditions (as defined in 30 CFR 
50.2), the employer is not required to 
report it to MSHA. Therefore, it should 
be noted that the statistics are based on 
reports of both lost-time and no-lost- 
time injuries, but that employers are not 
required to report certain types of no- 
lost-time injuries. 

After the injury report is received by 
MSHA's Health and Safety Analysis Center, 
much of the information on it is trans- 
formed into code numbers that correspond 
to predetermined categories. For exam- 
ple, there are a list of codes for de- 
scribing the types of acitivity miners 
were performing at the time they were in- 
jured. These code numbers are then en- 
tered into a computer file. Using a com- 
puterized retrieval system, information 



from this file can be selectively re- 
trieved and various types of statistics 
can be calculated. 

The primary goal of this paper is to 
use this information to identify the 
types of activities, objects, and condi- 
tions most frequently associated with the 
2,492 reported cases of an underground 
coal miner suffering a back sprain or 
strain during 1981. The first step to- 
ward this goal was to determine which 
categories for describing the type of 
accident were used most frequently. 

Ninety-seven percent of these injuries 
are categorized as one of three basic 
types of accidents: overexertion in at- 
tempting to move objects, falls to the 
ground, and jolts to the occupants of ve- 
hicles. In order to get a clearer pic- 
ture of the circumstances that often lead 
to each of these three types of acci- 
dents, the injuries within each major 
category were further broken down. De- 
pending upon which is more conducive to 
understanding the factors that may have 
contributed to the accident, the second 
level of breakdowns were based upon 
either the type of activity the miner was 
performing or the type of object that 
caused or contributed to the injury. 
Next, sets of descriptions of each acci- 
dent were retrieved for each group of in- 
juries that, on the basis of the second 



26 



level breakdown, accounted for more than 
1 pet of the total, i.e. , more than 24 
Injuries. These verbal accounts, called 
narratives, generally consist of one or 
two sentences describing what the miner 
was doing at or shortly before the time 
back pain was noticed. 

Included in the previously mentioned 
injury reports that mine operators file 
are written descriptions of how the acci- 
dent occurred. These narratives are also 
put into a computer file from which they 
can be selectively sorted into groups and 
retrieved. As mentioned earlier, sets of 
narratives were generated for each group 
of injuries accounting for more than 1 
pet of the total. 

Each of these groups of narratives was 
reviewed and a tally was kept of the 
types of activities, actions, environ- 
mental conditions, etc., that appear to 
have contributed to each miner's back in- 
jury. Conclusions based on these tallys 
are presented as each type of back injury 
accident is discussed. However, for a 
variety of reasons, these conclusions 



should be interpreted cautiously, as 
rough approximations to understanding 
what actually happened. In some cases, 
the injured miner or the individual who 
wrote the narrative may not have used the 
most accurate and descriptive language to 
convey what happened. For example, one 
narrative states that, "the miner hurt 
his back while moving cable," which does 
not indicate whether the miner was lift- 
ing, pulling, or hanging a cable. For- 
tunately, most narratives are more pre- 
cise in the language they use. 

It is recognized that in some cases, 
especially those involving back pain ow- 
ing to overexertion, it may be impossible 
for miners to pinpoint the event that 
caused their backs to hurt. The miner's 
back may have begun to hurt gradually 
over a period of time that he or she was 
performing a variety of activities, all 
of which contributed to overexertion of 
the back muscles. Although the narra- 
tives may be somewhat ambiguous and con- 
tain some error, they significantly im- 
prove one's ability to understand how 
miners commonly injure their backs. 



PRESENTATION OF THE DATA AND ITS IMPLICATIONS 



This section presents a detailed dis- 
cussion of each of the three major cate- 
gories of accidents. Each major type of 
accident is further broken down into sub- 
sets that possess some type of common 
element, such as similarities in the type 
of activity the victim was performing, 
the type of object with which the victim 
was working, or the type of bodily move- 
ment the miner was attempting at the time 
of the injury. As indicated in table 3, 
more back injuries were attributed to 
overexertion than to any other category 
for describing the type of accident. 
Although 79 pet were classified as in- 
juries because of overexertion, signifi- 
cant numbers were also classified as 
falls (11 pet) and jolts (7 pet). 



TABLE 3. - Back injuries suffered by 
underground coal miners during 1981 
by accident type 



Accident type 


Number of 
injuries 


Percentage 


Overexertion 

Falls 


1,958 

263 

183 

88 


79 
11 


Jolts 


7 


Other 


3 


Total 


2,492 


100 



OVEREXERTION IN MOVING OBJECTS 

Table 4 breaks down back injuries owing 
to overexertion by the types of objects 
miners were attempting to move. The most 
common types of objects being moved at 



27 



the time of a back injury were electric 
cables, broken rock and coal, timbers and 
posts, metal objects (not elsewhere 
classified), belt conveyors, wooden ob- 
jects (not elsewhere classified), steel 
rails, bagged material systems, jacks, 
mining machines, roof bolts, oil contain- 
ers, cement blocks, buckets and cans, 
metal covers and guards, pry bars, mo- 
tors, wheels, and boxes. As table 4 in- 
dicates, the movement of each of these 
categories of objects accounts for at 
least 1 pet of the total and, together, 
they account for 83 pet of all back in- 
juries due to overexertion. 

TABLE 4. - Overexertion back injuries 
suffered by underground coal miners 
during 1981, by the type of objects 
associated with the injury 



Type of object 


Number of 
injuries 


Percent- 
age 


Electric cables 

Broken rock and coal 
Timbers and posts... 

Metal objects' 

Belt conveyor 
systems ............ 


233 
231 
198 
156 

99 
82 
82 
82 
61 
49 
49 
48 
47 
46 

43 
33 
33 
32 
30 
324 


11.9 

11.8 

10.1 

8.0 

5.1 


Wood objects^ 

Steel rails 


4.2 
4.2 


Bagged materials.... 
Jacks ............... 


4.2 
3.1 


Mining machines 

Roof bolts 

Oil containers 

Cement blocks 

Buckets and cans.... 
Metal covers and 
guards ............. 


2.5 
2.5 
2.5 
2.4 
2.3 

2.1 


Pry bars ............ 


1.7 


Motors 


1.7 


Wheels 


1.6 


Boxes ............... 


1.5 


Other 


16.6 


Total 


1,958 


100.0 



'Does not include metal objects such as 
rails, roof bolts, jacks, motors, etc., 
that are listed in other categories. 

^Does not include timbers, posts, caps, 
and headers. 

Electric Cables . Based upon MSHA's 
categorization scheme, the movement of 
electric cables was associated with more 
back injuries due to overexertion than 



the movement of any other type of object. 
Forty-two percent of the narratives for 
these accidents indicate that the miner 
was pulling on a cable, 17 pet indicate 
that the miner was lifting a cable, and 
11 pet indicate that the miner was hang- 
ing or lowering a cable. The remaining 
narratives use less specific terms to de- 
scribe the miner's actions (e.g., moving 
or handling cable) or describe relatively 
unique types of accidents. 

Broken Rock and Coal. The second most 

coEimon category of object associated with 

overexertion injuries was broken rock and 

coal. The movement of rock and coal 

accounted for almost as many overexer- 
tion injuries as cables (11.9 versus 
11.8 pet). 

Approximately half of the narratives 
attribute the injury to shoveling and a 
quarter of the narratives attribute the 
injury to the manual lifting of broken 
rock and coal. The remaining narratives 
attribute the injury to other types of 
movement such as the dragging, rolling, 
or pulling of rocks. 

Timbers and Posts . The third most com- 
mon category of objects associated with 
overexertion injuries consisted of tim- 
bers, posts, caps, and headers. The nar- 
ratives refer to timbers and posts much 
more frequently than caps and headers. 
The types of movements most often men- 
tioned in the narratives are lifting, 37 
pet; loading and unloading, 16 pet; and 
throwing, 10 pet. The remaining narra- 
tives generally use less specific terms 
to describe the miner's actions such as 
setting, moving, or handling timber. The 
narratives usually describe back injuries 
due to throwing as "twist" of the back, 
suggesting that the injury occurs because 
miners often twist their body instead 
of pivoting on their foot when throwing 
timbers. 

Metal Objects (not elsewhere classi- 
fied). A review of the narratives indi- 
cates that there is no one specific type 
of metal object that accounts for a sig- 
nificant portion of the injuries in this 
category. The types of items mentioned 
include pipes, wire, coupling hitches, 



28 



ramps, and roof bolt augers. The types 
of movements most often mentioned in the 
narratives are lifting, 52 pet; loading 
and unloading, 10 pet; carrying, 10 pet. 

Belt Conve yor Systems . A review of the 
narratives indicates that the movement of 
each of three elements of belt conveyor 
systems was associated with roughly a 
quarter of the overexertion back injuries 
in this category. One of these elements 
is the belt structure. Narratives men- 
tioning belt structures usually state 
that miners were lifting, unloading, or 
carrying them when their backs were in- 
jured. A second element is rollers. 
Narratives mentioning rollers usually 
state that miners were lifting or chang- 
ing them when their backs were injured. 
The third element is the belt itself. 
Narratives mentioning belts usually state 
that miners were pulling, lifting, or 
loading belt material. 

Wooden Objects (not elsewhere classi- 
fied) . The types of items most often 
mentioned in the narratives for this cat- 
egory are crib blocks, boards, crossbars, 
planks, and props. Other than crib 
blocks, which account for almost half, no 
one specific type of wooden object is as- 
sociated with a significant portion of 
this category of injuries. Most narra- 
tives indicate that these injuries oc- 
curred as the object was being lifted. 

Steel Rails . About half of the narra- 
tives for this category of injuries indi- 
cate that the injury occurred while lift- 
ing rails. Most of the remaining inju- 
ries are attributed to loading, pulling, 
or pushing on rails. These accidents 
usually occur during the installation of 
rails as tracks or as roof supports. 

Bagged Materials . The narratives re- 
veal that three-quarters of the bags be- 
ing moved when the injury occurred con- 
tained rock dust, and that the others 
contained tools, cement mix, powder, and 
sand. Almost all the narratives state 
that the miner's back was injured while 
lifting or loading bags. A few narra- 
tives give the weight of the bag(s) that 
had been lifted when the injury occurred. 
Those which do, indicate that the rock 



dust bags weighed 50 lb, and that the 
bags of other materials were heavier, up 
to 100 lb each. 

Jacks . Most narratives for this cate- 
gory state that miners were lifting a 
jack when their backs were injured. How- 
ever, several narratives state that the 
miner was using a jack to remount de- 
railed vehicles when the back injury 
occurred. 

Mining Machines . This category of back 
injuries includes those suffered during 
the operation, maintenance, or repair of 
underground mining machines, but does not 
include injuries suffered while lifting 
motors or while riding or operating ve- 
hicles. The narratives indicate that 
approximately half of these injuries were 
associated with roof bolting machines. 
Several injuries are also attributed to 
lifting rock dust machines. 



Roof Bolts, 



About half of the narra- 



tives indicate that the back injury was 
received while the miner was unloading or 
lifting roof bolts. About one-third 
state that the miner was injured while 
attempting to bend a roof bolt. 

Oil Containers. Most narratives for 
this category of back injuries state that 
the injury occurred as barrels of oil 
were being lifted or loaded onto equip- 
ment. Several injuries occurred while 
oil was being poured into machinery and 
while miners were attempting to upright a 
barrel that was lying on its side. 



Cement Blocks. 



About half of the 



narratives for this category of back 
injuries indicate that the injury oc- 
curred as cement blocks were being lifted 
and/or carried. Roughly a quarter of 
the narratives state that the injury oc- 
curred while blocks were being loaded or 
unloaded. 

Buckets and Cans. Most narratives for 



this category of back injuries indicate 
that the injury occurred during the 
movement of buckets or cans of oil, 
grease, or water. Many narratives state 
that the bucket or can being moved was 
the 5-gal size. 



29 



Metal Covers and Guards . Most narra- 
tives for this category of back injuries 
reveal that the injury occurred during 
the removal or installation of the metal 
guards, covers, and canopies on under- 
ground powered equipment. The narratives 
also suggest that several of the back in- 
juries in this category occurred as bat- 
tery lids were being lifted. 



prolonged periods of time without rest. 
Shoveling can place unusually great 
stress on the back. Therefore, indi- 
viduals with a history of back problems 
should be especially careful not to over- 
exert themselves while shoveling. The 
data also suggest that miners should be 
discouraged from trying to throw objects 
as heavy and cumbersome as timbers. 



Pry Bars . Almost all narratives for 
this category of back injuries indicate 
that the miner was using a pry bar or 
crowbar to pry or lift on parts of 
machines or equipment. A small number 
attribute the injury to prying down loose 
top. 



Motors. 



The narratives for this cate- 



gory of back injuries generally state 
that the injury was received while at- 
tempting to lift an underground mining 
machine's motor. 

Wheels . Most narratives for this cate- 
gory of back injuries reveal that the in- 
jury occurred when tires were being load- 
ed or unloaded, or when a tire was being 
lifted onto a vehicle's wheel unit. 

Boxes . One and one-half percent of the 
overexertion back injuries were attrib- 
uted to the movement of boxes. The types 
of boxes mentioned most frequently in the 
narratives are toolboxes, dust boxes, and 
boxes of cutting bits for the continuous 
miner or bolter. 

IMPLICATIONS FOR PREVENTION 

The data suggest that there is an espe- 
cially great need to (1) improve upon 
present methods and equipment for manual- 
ly handling power cables, broken rock and 
coal, and timbers and posts in under- 
ground coal mines, or (2) find ways to 
lessen the amount of human (as opposed to 
mechanical) effort that must be devoted 
to handling these materials. The data 
also suggest that there is a need to 
prevent miners from using shovels in ways 
that are likely to place too much stress 
on the back. Miners should be discour- 
aged from using shovels to lift ob- 
jects that are too big, or shoveling for 



Potter2 presents tables of data con- 
cerning the recommended maximums for the 
amount of weight that should be lifted, 
pushed, or pulled by individuals accord- 
ing to their age and sex. He goes on 
to list the common weights of many of 
the objects that must be manually moved 
in underground coal mines, and points 
out that many of these objects exceed 
the recommended limits for most types 
of individuals. On the basis of these 
data. Potter suggests that several types 
of mining supplies and materials should 
be manufactured and packaged in smaller 
quantities. 

FALLING TO THE GROUND 

The second type of accident that ac- 
counts for a significant portion of min- 
ers' back injuries is falling to the 
ground. In 1981, 10.6 pet of the back 
injuries suffered by underground coal 
miners were the result of falling to the 
ground. Back injuries due to falls were 
further broken down by the activity the 
miner was performing at the time of the 
fall. The activities mentioned most fre- 
quently are walking, 26 pet, and handling 
supplies, 24 pet. Several miners also 
injured their backs while getting on or 
off equipment, handling timber, and mov- 
ing cable. However, in terms of the por- 
tion of total back injuries, the number 
associated with these last three activi- 
ties is relatively insignificant. There- 
fore, only falls associated with walking 
or handling supplies will be discussed. 

2potter, H. H. Back In juries--Causes 
and Cures. Pres. at Fall Meeting, See. 
Min. Eng. , AIME, Denver, CO, Nov. 18, 
1981, 10 pp.; available for consultation 
at MSHA's Division of Coal Mine Safety 
and Health, Denver, CO. 



30 



Walking . A review of the narratives 
for back, injuries associated with falls 
while walking reveals that most such ac- 
cidents were the result of slipping on 
mud or a wet surface. Other phases fre- 
quently used to describe the cause of 
falls are "stepping in a hole," and 
"tripping over" things on the ground. 

Handling Supplies . A review of nar- 
ratives for back injuries associated with 
falls while handling supplies reveals 
that such accidents were most frequent- 
ly the result of slipping on a wet or 
muddy surface while carrying something, 
or slipping while trying to pull on 
something. 



that they cause operators to strike their 
heads on the canopy above them. It would 
be possible to prevent some of these ac- 
cidents by doing the following: keeping 
the floor of the mine more level; cau- 
tioning shuttlecar operators to slow down 
for rough spots; increasing illumination 
of the mine floor, or providing some type 
of warning that signifies the presence 
of rough spots; putting cushions in the 
seat and on the canopy above the opera- 
tor; and requiring the use of seatbelts. 
It should be noted that these suggested 
solutions are by no means an exhaustive 
list, and that it may not yet be econom- 
ically feasible to implement some of 
them. 



Possible ways to prevent such accidents 
include keeping work areas as dry as pos- 
sible, keeping walking surfaces as level 
as possible and free of obstacles, im- 
proving illumination along walkways, and 
using boots with tread designs that pre- 
vent slipping on wet surfaces. 

JOLTS 

The third major type of accident re- 
sulting in back injuries consists of 
jolts to the occupants of underground ve- 
hicles. In 1981, 7.3 pet of the back in- 
juries suffered by underground coal min- 
ers were the result of the miner's body 
striking against a relatively stationary 
object. These injuries were further 
broken down by the activity being per- 
formed at the time of the accident. It 
was found that 28 pet of the victims of 
this category of accidents were operating 
a shuttle car, and 21 pet were riding in 
a mantrip or Jeep. 

Operating Shuttle Cars . A review of 
narratives for back injuries to the oper- 
ators of shuttle cars reveals that such 
injuries were almost always due to the 
operator being jolted when the shuttle 
car ran over a bump, hole, or rough spot 
in the mine floor. Some narratives de- 
scribe these jolts as being so severe 



Riding in Underground Transportation 
Vehicles . Back injuries suffered by the 
occupants of underground transportation 
vehicles were usually caused by one of 
two types of mishaps. The first type of 
mishap is that, like shuttle car opera- 
tors, miners received back injuries from 
being jolted when their vehicle ran over 
uneven places in the mine floor or in the 
tracks on which certain types of vehicles 
run. The second type of mishap, which 
caused as many back injuries as the 
first, was the collision of vehicles. 
Such collisions result in sudden jolts to 
the vehicle's occupants, sometimes caus- 
ing them to experience back pain. Many 
of the measures suggested for preventing 
back injuries to shuttle car operators 
would also be applicable to the operation 
of underground transportation vehicles. 
The following measures might also reduce 
the number of vehicle-related back inju- 
ries: encouraging miners to keep the 
roadways free of parked vehicles and 
other obstructions; encouraging vehicle 
operators to be more attentive to possi- 
ble obstructions in the roadway; and en- 
suring that vehicles, their brakes, and 
the track on which they run are properly 
maintained. Consideration might also be 
given to the use of better shock absorb- 
ing devices on these vehicles. 



31 



SUMMARY AND CONCLUSIONS 



A review of recent data on back, inju- 
ries suffered by underground coal miners 
suggests that many factors contribute to 
their occurrence. The action most fre- 
quently associated with these injuries is 
overexertion in lifting things. The 
types of things being lifted that are 
most frequently associated with back in- 
juries are cables, broken rock and coal, 
and timbers and posts. Another common 
form of overexertion causing back inju- 
ries is pulling on things. The object 
that causes the majority of back injuries 
due to pulling is power cables. Another 
activity associated with many back inju- 
ries due to overexertion is the shoveling 
of broken rock and coal. 

Although most back injuries are due to 
overexertion, a significant number of 
them are due to falls and jolts. The in- 
juries due to falls are typically the re- 
sult of slipping on a wet or muddy sur- 
face, or tripping over something while 
handling materials or while simply walk- 
ing. The injuries due to jolts are typi- 
cally the result of running over uneven 



places in the mine floor while riding in 
shuttle cars or underground transporta- 
tion vehicles. Another common type of 
mishap causing back injuries to the occu- 
pants of underground transportation ve- 
hicles is the collision of their vehicle 
into another vehicle. 

The fact that there are so many factors 
that contribute to underground miners' 
back injuries suggests that there are a 
variety of actions that could be taken to 
reduce back injuries, but that no one 
approach will be a panacea. The fact 
that most back injuries are the result of 
overexertion in the manual movement of 
things suggests that back injuries could 
be reduced most significantly by changing 
the way these things are moved, or elimi- 
nating the need to move some of them. 
Thus, although it is very important that 
more attention be devoted to the preven- 
tion of falls and jolts, there is an ex- 
tremely great need to devote more atten- 
tion to the prevention of overexertion 
injuries. 



32 



ANALYSIS OF COAL MINING BACK INJURY STATISTICS 
By Terrence J. Stobbel and Ralph W. Plummer2 



ABSTRACT 



Injury and illness in industry are at 
best complex problems. One of the big- 
gest of these problems is the overexer- 
tion injury. This is commonly character- 
ized as a strain or sprain injury. In 
its most severe form, it occurs to the 
back and necessitates disk surgery. 

This study collected and analyzed ex- 
isting data of job-related overexertion 



injury data for coal miners employed by a 
major coal company during the years 1977- 
82. The purpose of this analysis was to 
determine the magnitude of overexertion 
injuries, to determine the severity of 
the injuries, and to identify specific 
activities that account for large numbers 
of back injuries. 



INTRODUCTION 



The desire to control injury and ill- 
ness in coal mining is motivated by hu- 
manitarian and economic factors. The 
need to reduce pain and suffering not on- 
ly to the injured persons, but to their 
families and associates as well, is obvi- 
ous. The economic basis is perhaps less 
clear. The injured miner often loses a 
significant portion of his or her income 
while off the job. The employer pays the 
medical and indemnity costs of workmen's 
compensation, along with an equivalent 
amount in hidden costs, such as retrain- 
ing, administrative functions, etc. Coal 
mining is recognized as being one of the 
most hazardous industries. The high de- 
gree of hazard is reflected in the asso- 
ciated workmen's compensation costs. In 
West Virginia, underground coal mining 
has a base rate for compensation which is 
second only to high-rise structural steel 
work. The base rate, which is almost 
20 pet of payroll dollars, is more than 
twice the third place job activity — 
working in a sawmill. The base rate is 
adjusted up or down based on individual 
company experience and, as a result, some 
coal companies pay compensation premiums 
that are equal to three-fourths of pay- 
roll dollars. 

^President, S&P Associates, Morgantown, 
WV. 

^Vice president, S&P Associates, Mor- 
gantown, WV. 



Reduction of these costs is dependent 
on understanding their causes. One well- 
known cause is the overexertion injury. 
This type of injury ranges from strain 
and sprain to the more severe back injury 
that requires surgery. Nationally, these 
injuries account for 30 to 40 pet of all 
reported injuries, and at least as high a 
percentage of the compensation costs. 
Back injuries are a subset of these inju- 
ries, which account for about 20 pet of 
all reported injuries. 

The situation in coal mining is similar 
but worse. Accident statistics for West 
Virginia show that in 1979 back injuries 
accounted for 23 pet of all injuries. 
MSHA3 reported that, in 1980, back inju- 
ries accounted for 26 pet of all coal 
mining injuries. The associated compen- 
sation costs are estimated to be 30 to 40 
pet of the total compensation costs (for 
the company in this study). Having iden- 
tified the source of a significant por- 
tion of the coii^)ensation costs, we must 
look to understanding the cause of over- 
exertion and back injuries. 

In trying to understand the causes of 
these injuries, it is instrumental to 

-^Potter, H. H. Lack of Mechaniza- 
tion in Some Coal Mine Tasks. Mine Safe- 
ty and Health Magazine, Dec-Jan. 1982, 
pp. 8-13. 



33 



look first to general industry where 
most of the back injury related research 
has been. This research has shown that 
the major causes of back injury are mate- 
rials handling, slip-trip, and push-pull. 
Within these categories, materials han- 
dling predominates, and it is considered 
to be such a major problem that NIOSH has 
published a lengthy Work Practices Guide 
for Manual Lifting4 that summarizes what 
is currently known about the problem 
as well as providing control recommenda- 
tions. In essence, the guide reports 
that people who lift too much too often 
experience back and overexertion inju- 
ries. The guide then proposes a method 
for estimating relatively safe weights to 
lift under ideal lifting conditions. 

Looking now at coal mining, it is again 
found that the situation is similar but 
worse. Materials handling is a major ac- 
tivity in the mines, and in most mines it 
is increasing in frequency as the rate of 
mining coal increases. 5 Loads handled 
are equal to or heavier than those han- 
dled in general industry. Typical "man- 
handled" loads are shown in table 1. The 
work practice guide emphasizes that 
its recommendations apply to ideal lift- 
ing conditions. However, lifting condi- 
tions in coal mining are far from ideal. 
Loads are bulky and do not have handles, 
and furthermore, floor conditions vary 
from dry and uneven to wet, muddy, and 
slippery. 

TABLE 1. - Weights of materials commonly 
handled in coal mines 

Materials lb 
Roof bolts: 

5/8 in by 6 ft, bundle of 10 55 

5/8 in by 10 ft, bundle of 10 90 

Crossbar, oak, 4 by 6 in by 16 ft... 129 

Round post, oak, 6-in diam by 6 ft.. 57 

Concrete block, 8 by 8 by 16 62 

Cement, 1 bag 80 

Rock dust, 1 bag 50 

Rail, 30 lb, 30-ft length 300 

^. S. Department of Health and Human 
Services. Work Practices Guide for Man- 
ual Lifting. NIOSH Pub. 81-122, 1981, 
183 pp.; NTIS PB 82-178-948. 

^Work cited in footnote 3. 



With respect to the above, the Bureau 
of Mines sponsored this study of coal 
mining back injuries. To the extent pos- 
sible, this description includes such 
factors as job, task, materials handled, 
mine height, time of year, repeated inju- 
ries to the same miner, and exposure 
hours. 

The results of this study are aimed at 
reducing back injuries in coal mining. 
This will be accomplished by applying the 
result of this study to (1) identifying 
specific jobs with high back injury fre- 
quency rates based on hours of exposure 
(work); (2) conducting job safety and 
physical stress anslyses of these jobs to 
isolate specific tasks or work procedures 
that increase the risk of back injury; 
(3) isolating tools, supplies, equipment, 
etc. , that act as causes or agents in a 
significant number of back injury scenar- 
ios; and (4) redesigning or modifying the 
tasks, work procedures, tools, supplies, 
or equipment that significantly increase 
back injuries. 

METHODOLOGY 

The purpose of this research was to 
develop a set of statistics that would 
describe the back injury problem in coal 
mining in sufficient detail so that 
future research directions could be 
identified. Two sources of data were 
available: the MSHA's Health and Safety 
Analysis Center (HSAC) data base and in- 
dividual company accident-injury records. 
Each data base had advantages to its use. 
HSAC records covered all of the mining 
industry, thus a larger data base was 
available. They were, however, based on 
a single reporting form, and their ac- 
curacy suffered to the extent that dif- 
ferent companies and mines use different 
titles to describe the same job or activ- 
ity or the same title to describe differ- 
ent jobs and activities. Individual com- 
pany records were limited in that a much 
smaller data base was available, but they 
were superior because considerable back- 
ground information was available beyond 
the HSAC reporting form. In addition, a 
comprehensive review of a large coal pro- 
ducer's back injury statistics was not 
available in the literature. 



34 



In view of the above, individual com- 
pany statistics were used. Contact was 
made with a large coal producer and after 
some discussion it was agreed that the 
analysis would be mutually beneficial. 
Access was provided to all of the com- 
pany's accident records. This included 
the company's internal first injury re- 
port, the HSAC form, the company's inter- 
nal statistical report, and miscellaneous 
data that found their way into individual 
accident files. All of these data were 
reviewed for the 6-yr period 1977-82, 
during which a total of 974 back injuries 
were reported. Correct interpretation of 
the data required frequent contact with 
company personnel in a number of areas 
including the medical department, safety 
department (corporate and field) , mine 
supervision, industrial relations, com- 
pensation, and industrial engineering. 

The review of the accident data pro- 
vided an excellent description of the 
nature, source, and frequency of back, 
injuries, but without exposure data, it 
was difficult to interpret. Exposure 
data were collected with the additional 
help of the company's industrial engi- 
neering group. As expected, collection 
and interpretation of both exposure and 
accident data were difficult since there 
were numerous mine-to-mine inconsisten- 
cies in the titles placed on jobs and 
activities. These inconsistencies were 
identifiable only with the help of com- 
pany personnel. 

The actual data collection process in- 
volved reading all of the information 
contained in each accident file and cod- 
ing it for later analyzing using a sta- 
tistical analysis system (SAS). The fol- 
lowing is a partial list of the data 
collected. 

Bureau of Mines identification. 

Primary cause. 

Secondary cause. 

Agent of injury. 

Sex of injured miner. 



Total mining experience. 

Permanent job classification. 

Date injury occurred. 

Time of day injury occurred. 

Date injury reported. 

Job being performed when injury 
occurred. 

Total experience in job being performed 
when injured. 

Part of body injured. 

The unique feature of this data set is 
the inclusion of the primary and second- 
ary causes of the injury, as well as the 
agent of injury. Partial lists of these 
variables are provided in the following 
tabulations. 

Primary cause: 

Lifting-twisting Jumping from 

vehicle. 



Tripped 

Slipped 

Pulling 

Fell 

Shoveling 

Stumbled 



Carrying 

Pushing 

Hit canopy 

Prying 

Hit bump (vehicle) 

Twisting 



Hit rough road Pulling down 

(vehicle) Hit by object 

Bend over and/or Handling supplies 

lifting. Striking head 

Secondary cause ; 

Crib block Supply car 

Swinging pick Walking 

Landed on seat Unbalanced load 



35 



Secondary cause — Continued: 

Lifted over head Slipped 

Timber Roof bolter 

Absence of guard Fell against post 

Wet area Blasting 

Operating motor Climbing ladder 

Twisted body Slipped on a rock 

Climbing railroad Fan house 
car. 



Agent category : 
Steel rope 
Plank 
Stone falls 



Bag of rock dust 
Trolley wire 
Railroad ties 



Concrete blocks Chunk of coal 

Hit canopy Culvert pipe 

Pry bar Straighten up 

Shoveling Drill unit 

Hit roof bolt Post 

Air jack Stepped in hole 

Jarred Using a wrench 
Primary cause ; 

Lifting-twisting Carrying 

Tripped Pushing 

Slipped Hit canopy 

Pulling Prying 

Fell Hit bump (vehicle) 

Shoveling Twisting 

Stumbled Pulling down 



Primary cause — Continued: 

Hit rough road Hit by object 
(vehicle). 

Bend over and/or Handling supplies 
lifting. 

Jumping from Striking head 
vehicle. 

Secondary cause : 

Crib block Supply car 

Swinging pick Walking 

Landed on seat Unbalanced load 

Lifting over head Slipped 

Timber Roof bolter 

Absence of guard Fell against post 

Wet area Blasting 

Operator motor Climbing ladder 

Twisted body Slipped on a rock 

Climbing railroad Fan house 
car. 

Agent category ; 

Steel rope Bag of rock dust 

Plank Trolley wire 

Stone falls Railroad ties 

Concrete blocks Chunk of coal 

Hit canopy Culvert pipe 

Pry bar Straighten up 

Shoveling Drill unit 

Hit roof bolt Post 

Air jack Stepped in hole 

Jarred Using a wrench 



36 



Use of this multiple coding scheme 
allowed the subsequent analysis to go 
beyond the usual analysis which reveals 
that X people were injured lifting, 
Y pulling, etc. ; G people were handling 
timbers, H bags, etc. Instead it was 
possible to identify the number injured 
by lifting by each agent category. Fur- 
thermore, this approach permitted the 
identification of those situations in 
which the person was lifting a timber 
and slipped. Clearly, it is not known 
whether it was the lift or the slip 
that caused the injury, but the fact 
that they were lifting a heavy object 
when they slipped certainly contributed 
to the injury. The slip would probably 
not have occurred without the force dy- 
namics that lifting places on the body, 
and the injury may not have occurred 
without the sudden body movement owing to 
the slip. In most conventional data 
analyses, this would be coded simply as 



a lift or a slip and the joint cause 
would be lost. 

In addition to developing the descrip- 
tive statistics, the effects of mine 
height, the contribution of back injury 
repeaters to the overall problem, and the 
often repeated argument that people take 
advantage of the back injury to get a few 
days off during hunting season were stud- 
ied. Mine height was provided by indus- 
trial engineering and grouped into four 
categories. Where meaningful, the data 
were statistically analyzed to determine 
which conditions were significant. 

There is one element not included in 
this discussion — cost data. At the time 
of writing, this information was still 
being prepared by the compensation de- 
partment. When received and analyzed 
this will make a valuable addition to 
this study. 



RESULTS 



The comprehensive review of 6 yr of 
back injury data results in a massive 
amount of data. It is not practical to 
describe all of it in a single paper. 
Rather, this paper will present the re- 
sults of selected analyses. The report- 
ing order will be to report the mixed-job 
statistics first, followed by in-depth 
analyses of selected jobs. The preva- 
lence of back injuries in coal mining was 
discussed in the introduction. From a 
control standpoint, the more interesting 
question is who suffers these injuries. 
When the question is discussed with min- 
ing management, it becomes clear that a 
mystique has developed about back inju- 
ries within which the persons concerned 
have developed their own theories of 
causation, often without supporting data. 
Common examples which were suggested fre- 
quently included 

1. They lift the wrong way. 

2. They try to lift too much. 

3. There is always a rash of them when 
the miners want a few days off. 

4. It is the same miners who get hurt 
over and over again. 



The data analyzed herein do not address 
the first two issues, so all that can be 
done is to point out that there is no 
single best way to lift. The "lifting 
method is dependent on the nature of the 
load and environmental circumstances sur- 
rounding the lift, "6 With respect to the 
size of the lift, it is true that miners 
often lift too much — but who is responsi- 
ble? Who designs the jobs, specifies the 
weights of supplies, and determines the 
work pace? Furthermore, how is an indi- 
vidual miner supposed to know how much he 
or she can lift? 

There were data available in this study 
to address issues 3 and 4. The use of a 
back injury to selectively obtain extra 
time off is supposedly one with some fre- 
quency. In the mystique, hunting season 
is the prime time for convenient back in- 
juries. To evaluate the issue, contact 
was made with the Natural Resources De- 
partments of the States in which injuries 
were reported to identify the dates of 
hunting season during the years studied. 
The mean number of back injuries that oc- 
curred during hunting season was com- 
puted and compared year by year to the 

^Work cited in footnote 4. 



37 



in table 2, show 
mystique is wrong. 



mean number of back injuries occurring on 
any other day of the year. The week pre- 
ceding hunting season was included with 
the hunting data. The results, presented 
that the conventional 
The statistical anal- 
ysis demonstrates that there are fewer 
back injuries per day just before and 
during hunting season, than during the 
rest of the year. 

TABLE 2. - Comparison of back injury 
rate (BIR) preceding and during 
hunting season with the BIR during 
the rest of the year 



frequency rate for mining jobs with high 
back injury frequencies. The frequency 
provides a relative comparison of the 
magnitude of the problem per job, while 
the frequency rate indicates the likeli- 
hood of getting hurt on a given job by 
adjusting the frequency for exposure 
hours. As expected, those jobs requiring 
considerable manual materials handling 
are the jobs with the highest rates. The 
possible exception to this is the shuttle 
car operator. 

TABLE 4. - Comparison of frequency and 
frequency rates for coal mining jobs 



BIR — hunting. . . . 
BIR — nonhunting. 



Mean 



0.312 
.418 



Variance 



0.223 
.488 



NOTE. — T-test calculated = 2.262. T- 
test tabular value = 1.645 for a = 0.05. 

Issue 4, back injury repeaters, also 
proved to be more mystique than fact. 
Table 3 presents the number of injuries 
per miner during the 6-yr period. Re- 
peated back injuries, at least during 
the time period studied, were infrequent. 
The data were examined further to see 
if there was a pattern to the timing of 
injuries in the repeater, and none was 
found. The distribution of job titles 
among the repeaters was consistent with 
that of the overall study. 

TABLE 3. - Frequency of back injuries 
per miner during the 6-yr period 
1977-82 

Number of miners Injuries 

10,000 

882 1 

40 2 

4 3 

The next section of the report ad- 
dresses the questions of which jobs 
have a high frequency of back injuries 
and what causes them (doing what) . Ta- 
ble 4 presents the injury frequency and 





Frequency, 


Frequency 


Job title 


number of 


rate per 




injuries 


thousand h 


Laborer. .......... 


158 
41 


37.05 


Trackman-helper. . . 


29.42 


Brattice worker. . . 


18 


18.30 


Shuttle car 






operator. ........ 


95 
129 


15.74 


Mechanic-helper. . . 


13.22 


Continuous miner 






operator-helper. . 


54 


10.73 


Roof bolter-helper 


67 


10.29 



In addition to looking at jobs, this 
study reviewed causes (activities at the 
time of injury), and agents (things han- 
dled or producing the injury). Table 5 
presents an overview of the cause of 
injury. Clearly, materials handling- 
related injuries dominate the list. The 
materials handling category includes 
lifting of all forms (carrying, twisting, 
bending, single- and two-person lift, 
etc.). Table 6 presents an overview of 
the agent handled at the time of injury. 
In this case, no one category stands out. 
Handling supplies such as bagged or 
drummed materials and concrete blocks is 
the most frequent, but back injuries due 
to riding in vehicles, handling timbers, 
planks and posts, and cable handling are 
close behind. The data presented in 
table 6 are consistent with the high fre- 
quency of materials handling-related in- 
juries found in table 5. 



38 



TABLE 5. - High-frequency causes of back 
injury in coal mining 

Causes Frequency 

Lifting^ 158 

Lift-twist' 107 

Slip-trip 107 

Push-pull 93 

Bend lift' 41 

Hit by object 41 

Working 24 

Unload ' 19 

Operating machine 18 

' Several causes were combined to form 
materials handling. 

TABLE 6. - High-frequency agents of back 
injury in coal mining 

Agents Frequency 

Handling general supplies 101 

Planks, timbers 91 

Riding in vehicle 90 

Cables 84 

Railroad related 69 

Tools 57 

Shovel, wheelbarrow 52 

The data in tables 5 and 6 can be 
broken down further by investigating 
the relationship between cause and agent. 
Table 7 provides a frequency distribu- 
tion for agents associated with materi- 
als handling. Table 8 provides agents 
for slip-trip, and table 9 for push-pull. 
Each cause of injury has its own dominant 
agents. 

TABLE 7. - Frequency distribution for 
agents of materials handling' injuries 



TABLE 8. - Frequency distribution for 
agents of slip-trip' injuries 

Agent Frequency 

Floor conditions 69 

Tools and equipment 13 

Railroad related 12 

Supplies 7 

Stairs 5 

Planks and timbers 4 

' Primary cause of 138 back injuries. 

TABLE 9. - Frequency distribution for 
agents of push-pull' injuries 



Agent 



Frequency 



Agent 



Frequency 



Cable 35 

Building supplies 12 

Tools and equipment 12 

Wheelbarrow 10 

Hose 6 

Steelrope 4 

'Primary cause of 93 back injuries. 

The preceding discussion has analyzed 
the overall back injury data for a ma- 
jor coal company. The balance of this 
section will provide examples of the 
analysis of job-related injury data by 
analyzing two of the jobs in detail. 
In essence, this means breaking down 
the cause and agent data for two jobs: 
laborer and shuttle car operator. Of 
the mining jobs, the laborer job had 
both the highest frequency and frequency 
rate. Table 10 shows the frequency dis- 
tribution of causes of back injury for 
laborers. The laborer's job consists of 
setting posts and timbers, laying and 
retrieving rails, unloading supplies, 
shoveling, general cleaning activities, 
etc. 



Planks and timbers 70 

Tools and equipment (timber 

jacks, 21) 69 

Supplies 48 

Railroad ties-bars 42 

Shovel-rocks 41 

Cables 38 

Bagged materials 28 

Drums -cans 18 

Wheelbarrow 11 

Belts-belt drive 11 

' Primary cause of 428 back injuries. 



TABLE 10. - Causes of laborer back 
injuries 

(Total cases, 158; frequency rate, 37.05) 



Cause 

Slip-trip 

Riding in vehicle.. 
Materials handling. 
Push-pull 



pet 




39 



As would be expected, more than half of 
the Injuries are the result of materials 
handling or push-pull activities. Anoth- 
er 18 pet are due to slips-trips, but 
when these are analyzed further, a third 
of them involve materials handling. The 
remaining injuries are split between 
shoveling and riding in vehicles. Shov- 
eling is to some extent a variation of 
materials handling, but having 12 pet of 
laborer's back injuries associated with 
riding in vehicles raises some serious 
questions about mine vehicle design. A 
more detailed breakdown of laborer in- 
juries is provided in table 11 by materi- 
als handling, slip-trip, and riding in 
vehicle. 

TABLE 11. - Analysis of activity at time 
of laborer injury 



the balance of the injuries. Again, al- 
most one-third of the slip-trip injuries 
involved materials handling. The high 
percentage of vehicle-related injuries is 
perhaps not surprising for a vehicle op- 
erator, but it again suggests problems 
within vehicle design, particularly as it 
relates to occupant safety. When com- 
pared with the estimated job exposure, 
the high frequency of materials handling 
injuries raises a question about the re- 
lation among the shuttle car operator's 
seat design, the constant forward flexed 
posture and vibration exposure, and a 
predisposition to lifting injuries. 

TABLE 12. - Causes of shuttle car 
operator back injuries 

(Total cases, 95; frequency rate, 15.74) 



Activity 



Frequency | pcF 



MATERIALS HANDLING 






Timber, plank, railroad 
ties 


18 
12 
11 

11 

4 

20 


24 


Shovel 

Rair bars 


16 

14 


Supplies, bagged materi- 
als, concrete blocks.... 
Cable 


14 
5 


Other 


26 



SLIP-TRIP 



Floor conditions... 
Materials handling. 

Using tools 

Others 




48 

34 

11 

7 



RIDING IN VEHICLE 






Floor conditions ......... 


6 
6 
5 
2 


32 


Collision 


32 


Hit object 


26 


Derail 


10 







A similar analysis is provided for the 
shuttle car operator (tables 12-13). 
This job was selected because of its con- 
trast to the laborer. In theory, this 
job involves considerably less materials 
handling and, in fact, industrial engi- 
neering estimated that only 15 to 20 pet 
of the job is materials handling (com- 
pared with 40 to 45 pet for laborer) . In 
spite of this, when push-pull is added to 
strict materials handling, 53 pet of the 
back injuries are accounted for. Riding 
in vehicles accounts for 29 pet, with 
slip/trip and shoveling accounting for 



Cause 

Slip-trip 

Riding in vehicle. , 
Materials handling. 

Push-pull 

Shoveling 




pet 



11 

29 

46 

9 

5 



TABLE 13. - Analysis of shuttle car 
operator activity at time of injury 



Activity 



Frequency | pet 



MATERIALS HANDLING (INCLUDES PUSH-PULL 
AND SHOVELING) 



Timbers , 

Cables , 

Bagged materials, 

Supplies , 

Shoveling , 

Wheelbarrow , 

Timber j acks 

Other 



10 
10 
7 
6 
5 
5 
2 
12 



18 

18 

12 

11 

9 

9 

4 

21 



RIDING IN VEHICLE 



Floor condition. 

Collision 

Other 



20 
5 
3 



71 
18 
11 



SLIP-TRIP 



Floor condition. . . . 
Materials handling. 
Other 



50 
30 
20 



A final issue of interest is the effect 
of mine height. Table 14 presents a com- 
parison of the frequency rates associated 
with the four mine height categories used 
in this study. The higher ranges were 



40 



selected based upon ease of categoriza- 
tion from the company's records. The 
data should be interpreted with caution 
since four or less mines are represented 
in each of the first three categories. 
The data in the first three categories 
were pooled to determine whether there 

TABLE 14. - Comparison of back injury 
frequency rates by mine seam height 
for one company 

Mine seam height, in Frequency rate 

<48 7.51 

48 to 60 10.87 

60 to 78 4.90 

>78 16.61 

CONCLUSIONS AND 

This paper has provided an overview of 
a rather massive data collection effort 
designed to probe the circumstances sur- 
rounding back injuries in coal mining. 
A short paper could not do more than sum- 
marize the subject and introduce one 
method for analyzing the problem. It be- 
gan by evaluating some of the convention- 
al wisdom and opinions about back inju- 
ries in coal mining, and established that 
for this company, the wisdom was in con- 
flict with the facts. The problems that 
lead to back injuries are complex, and 
hese results clearly suggest that the fi- 
rst steps in solving the problem will 
have to be thorough, quantitative analy- 
ses of the situation and not, as has of- 
ten been done, a reliance on conventional 
wisdom and opinion. We cannot ever do 
away with back injuries, but by system- 
atically analyzing the problem, and con- 
trolling what is done, how it is done, 
and who does it, it should be possible to 
achieve a significant reduction in the 
back injury rate. 

The overall pattern of back injuries 
was analyzed, and it pointed to a number 
of conditions as being the source of the 
problem. The primary source was, as ex- 
pected, materials handling. This is con- 
sistent with similar analyses performed 
in general industry. Additional indepth 
analyses conducted on specific jobs also 
identified materials handling as a major 
problem, but these also highlighted 
vehicle-related injuries, often the re- 
sult of hitting bumps in the haulageway. 



appeared to be differences between mines 
in which miners work standing (>78 in) 
and those which preclude standing (table 
15). The rates suggest that standing is 
more hazardous, but with only three data 
points to compare, the differences were 
nonsignificant. 

TABLE 15. - Comparison of back injury 
frequency rates in mines greater than 
and less than 78 in for one company 



Year 


Mine height, in 




<78 


>78 


1980 


6.5 
3.4 
6.2 


20.2 


1981 


13.7 


1982 


8.3 


Average 


5.4 


14.2 



RECOMMENDATIONS 

as being a significant cause. Identifi- 
cation of materials handling as a problem 
is not a new insight. MSHA's Hershel 
Potter stated it was a problem years ago. 
What is new in this research is the po- 
tential for a job-by-job breakdown of the 
pattern of back injuries to determine 
what approach may work on each job. The 
other new feature of this effort will be 
that of tying together the costs and in- 
juries so that both frequent and costly 
injuries can be examined. The next step 
in this process will be application of 
these data to the jobs studied to find 
practical ways of modifying either job or 
agent to reduce the risk of injury. 

Identifying vehicle riding as a major 
source of back injury suggests a number 
of promising research directions. At 
this point, the cause appears to be a 
combination of forward flexed posture, 
continual vibration exposure, and occa- 
sional severe jarring which combined to 
create the injuries. In addition, it ap- 
pears they form a predisposition to lift- 
ing injuries. Much of this relates di- 
rectly to vehicle design and, as such, is 
a problem that management can control. 

The analyses reported here will be ex- 
panded for use in working with company 
engineers, supervisors, and miners to de- 
crease the injury frequency rate. Future 
reports will provide a description of one 
or more innovations that have resulted in 
the decrease of back injuries among coal 
miners. 



41 



TWO BACK RISKS IN MINING: LIFTING AND PUSHING AND PULLING 
By Robert 0. Andres 1 



INTRODUCTION 



Mining has long had the onus of being 
one of the most hazardous occupations for 
the workers involved. The nature of the 
work, is quite physical, and many of the 
accidents are unpredictable owing to 
falling roofs or materials. There were 
about 40,000 disabling injuries in 1974 
for the mining and quarrying industries 
(11) ,2 and out of 41 industries reporting 
to the National Safety Council, under- 
ground coal mining had the highest fre- 
quency rate and severity rate (35.44 dis- 
abling injuries and 5,154 days lost per 
1,000,000 employee-hours, respectively). 
However, not all of these injuries are 
due to falls of mine roofs; slips and 
falls on the same level and materials 
handling showed up as causes of injury 
also in mining (14). Broken down on the 



basis of part of the body injured, from 
33 to 42 pet of the injuries reported 
(from underground to open-pit mining) 
were to the trunk. Between 33 and 44 pet 
of the total injuries were strains and 
sprains due to overexertion. These find- 
ings for the mining industry echo the 
statistics for the workplace in general, 
where 27 pet of all injuries occurred to 
the trunk, resulting in 38 pet of the to- 
tal workmen's compensation in 1974 (11). 

Recent research has been concentrating 
on the risks of back injury during manual 
materials handling, and also during dy- 
namic pushing-pulling. Some of this re- 
search and its methodologies will be de- 
scribed briefly, and example applications 
to the mining industry will be presented. 



BIOMECHANICS OF THE LOW BACK 



Epidemiological studies have shown that 
the low back is a structural weak link in 
the musculoskeletal system. Approximate- 
ly 80 pet of back injuries occur in the 
L4-L5 or Lj-S^ region of the spine (,1) • 
A large body of evidence indicates that 
many of these back injuries result from 
excessive compressive forces on the L5~S, 
disk (_2, 9-10). Cadaver studies have 
shown that compressive forces in excess 
of 1,500 lb result in L^-S , disk verte- 
brae failures in cadavers of males 40 yr 
old or younger (_6, 13). This load level 
decreases with age, and females have 
an even lower tolerance. Low-back pain 

''Assistant research scientist. Center 
for Ergonomics, University of Michigan, 
Ann Arbor, MI. 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



incidents have been shown to increase 
with predicted compressive forces on the 
L5-S , disk (_5) , so the biomechanics of 
the low-back region will be examined in 
more detail. 



Figure 1 is a free body diagram of the 
torso showing the different forces that 
contribute to the compressive force on 
the L5-S , disk. Only the abdominal force 
exerted on the diaphragm counteracts the 
forces due to the upper body mass, the 
load in the hands, and the forces of the 
trunk extensor muscles (erector spinas). 
Static analysis of this situation solves 
for the L5SO, compressive force; this 
static model has been applied to load 
handling by several researchers (^~^. ]_) • 
Given the body posture, the weight of the 
load in the hands, and the position of 
the hands, these models can predict the 
compressive force on the L5-S ^ disk. 



42 



NIOSH WORK PRACTICES GUIDE 



One culmination of the biomechanical 
approach to studying low-back injuries 
was the development of the "Work. Prac- 
tices Guide for Manual Lifting" by NIOSH 
( 13 ) in 1981. This document combines 
epidemiological, biomechanical, physio- 
logical, and psychophysical research re- 
sults to make recommendations about lift- 
ing. This amalgamated approach does not 
pretend to be the final word on lifting 
techniques; in fact, the major recommen- 
dation is that much more research in 
all of these areas is necessary, but 
there are several interesting analyses 
that can and should be applied to jobs as 
stressful as those found in the mining 
industry. 

Two different lifting limits have been 
defined in the guide: The maximal per- 
missible limit (MPL) above which load the 
lift is so hazardous that only a few 
people could perform it safely, and the 
action limit (AL) above which weaker in- 
dividuals are at risk, but most people 
can safely perform the lift. When ex- 
ceeded, the MPL dictates that job re- 
design must be performed, whereas exceed- 
ing the AL requires aggressive selection 
and training procedures to protect those 
at risk. Figure 2 shows the maximum 



weight that can be lifted (in a sym- 
metric, sagittal plane, two-handed lift) 
infrequently (once every 5 min) from 
floor-to-knuckle height as a function of 
the horizontal location of the load. The 
criteria that defined the MPL include (1) 
epidemiology, musculoskeletal injury and 
severity rates increase in populations 
performing work above this level; (2) 
biomechanics, conditions above the MPL 
result in L^-S ^ compressive forces above 
1,400 lb, which is not tolerable to most 
workers; (3) physiology, metabolic rates 
would exceed 5.0 kcal/min for most indi- 
viduals above the MPL; and (4) psycho- 
physics, only 25 pet of male and less 
than 1 pet of female workers have the 
muscle strength to work above the MPL. 
These same criteria, applied for the AL, 
show (1) only a moderate increase in in- 
jury and severity rates, (2) a 770-lb 
compressive force on the L5~S ^ disk, 
which can be tolerated by most young, 
healthy workers, (3) metabolic rates ex- 
ceeding 3.5 kcal/min for most people 
working above the AL, and (4) 99 pet of 
men and over 75 pet of women could lift 
loads described by the AL. 

The following algebraic formula was de- 
rived to calculate the AL: 



Al(lb) = 90(6/H)(1-0.01|V-30|)(0.7+3/D(1-F/Fmax) 

where H = horizontal location forward of midpoint between ankles at lift origin, or 
inches, 

V = vertical location at lift origin, inches, 

D = vertical travel distance between lift origin and destination, inches, 

F = average lift frequency, lifts per minutes, 

F^^^^ = maximum frequency which can be sustained (table I), 

then MPL = 3 (AL). 

See reference 13 for the limits of application to a mining situation will be 
these variables. With this brief in- presented, 
troduction to the guide, an example 



EXAMPLE APPLICATION 

Figure 3 schematically represents a 
situation where a miner lifts rock, or 
coal from the mine floor to a waiting 



43 



cart. Assuming this takes place fre- 
quently throughout an 8-hr shift, Fn^^^=12 
(table 1). If the lift is performed once 
per minute (F=l), the results for just 
the vertical portion of the lift are 



AL(lb) = 40(6/18)(l-0.004|7.6-75|)(0.7+7.5/20)(l-l/12) 
= 40(0. 333)(1.26)(1.075)(0. 917) = 16.54 lb 
MPL = 50 lb 



TABLE 1. - Maximum sustained lifting 
frequency 



Period, h 


Average vertical location, in 




>30, standing 


<30, stooped 


1 


18 
15 


15 


8 


12 



Therefore, any load material smaller 
than 16 lb should not overly stress 
any worker, whereas loads between 16 to 
50 lb should only be handled by stronger 



workers with care, and loads above 50 lb 
should not be lifted. The control mea- 
sure in this situation would be breaking 
the rock up into pieces smaller than 16 
lb. If this lift were performed up to 
five times a minute, the AL would be 
10 lb while the MPL would be 30 lb. 
Although few actual tasks are as simple 
to analyze as this one, this type of 
analysis is obviously quite easy to per- 
form as a first attempt to control job 
stresses. 



CART PUSHING AND PULLING 



In some mining operations the mined 
material is loaded on carts, sometimes on 
rails, which are then manully manuevered. 
This situation can lead not only to mus- 
culoskeletal strains or sprains, but also 
to slips or falls owing to inadequate co- 
efficient of friction parameters at the 
shoe-floor interface. A biodynamic model 
has been developed i8) that predicts the 
risk of low back injury and the risk of 
foot slip. This model is not restricted 
to static push-pull tasks, but only oper- 
ates in the sagittal plane. The inputs 
to the computer model are subject an- 
thropometry, body joint motion data, cart 
handle height, and the forces exerted by 
the hands on the cart handles. 

Figure 4 is an illustration of the lab- 
oratory equipment used to gather the mod- 
el inputs. The model then calculates the 
reactive forces and moments at each 
joint, the L^-S^ compressive load, and 
the required coefficient of friction to 
prevent foot slip. Although this model 
is still being refined and validated in 
the laboratory, it will be applied exten- 
sively in the field. Example predictions 



from the model are shown in figures 5 and 
6. Figure 5 illustrates the predicted 
Lg-S^ compressive forces for an example 
push-pull situation, while figure 6 is an 
example of predicted coefficient of fric- 
tion requirements at the shoe-floor in- 
terface during a push. 

Field data taken with portable force 
measuring handles and high-speed movies 
will be run through the biodynamic model 
to obtain output similar to figures 5 and 
6. From this analysis the following rec- 
ommendations can be made: (1) The maxi- 
mum allowable hand forces, which relate 
to cart loading and resistance; (2) the 
required coefficient of friction, which 
relates to the shoe and floor materials, 
shoe tread design, floor surface prepara- 
tion, and floor maintenance; (3) cart 
handle placement to minimize back injury 
risk (this changes for pushing versus 
pulling); and (4) the required strength 
of the worker performing the task. Al- 
though this model is still being refined, 
it represents another tool that should be 
used to analyze the stresses of physical 
work. 



44 



SUMMARY AND CONCLUSIONS 



There are several recently developed 
analytical tools available for study- 
ing working situations, such as mining, 
that have high musculoskeletal injury 
rates and severity rates. Only two tech- 
niques of predicting overexertion inju- 
ries to the low back have been discussed 
in this paper, along with some example 



applications to mining. As research pro- 
gresses in ergonomics, more use must be 
made of its results by the industries 
that can benefit most from its applica- 
tions; hence, a unique possibility for 
cooperation among academia, management, 
and labor exists and should be pursued. 



REFERENCES 



1. Armstrong, J. R. Lumbar Disk Le- 
sions. Williams and Wilkins, Baltimore, 
MD, 1965, pp. 230-239. 

2. Chaffin, D. B. A Computerized Bio- 
mechanical Model: Development of and Use 
in Studying Gross Body Actions. J. Bio- 
mechanics, V. 2, Oct. 1969, pp. 429-441. 

3. . On the Validity of Biome- 

chanical Models of the Low Back for 
Weight Lifting Analysis. Pres. at the 
Winter Ann. Meeting of ASME, Houston, TX, 
Nov. 30-Dec. 4, 1975; available upon re- 
quest from R. 0. Andres, Univ. MI, Ann 
Arbor, MI. 



8. Lee, K. S. Biomechanical Modelling 
of Cart Pushing and Pulling. Ph.D. Dis- 
sertation in Industrial and Operations 
Engineering, Univ. MI, Ann Arbor, MI, 
1982. 

9. Martin, J. B., and D. B. Chaffin. 
Biomechanical Computerized Simulation 
of Human Strength in Sagittal-Plane 
Activities. AIEE Trans., v. 4, 1972, 
pp. 19-28. 

10. Morris, J. M. , D. B. Lucas, and 
B. Bresler. Role of the Trunk in Stabil- 
ity of the Spine. J. Bone Joint Surg. , 
V. 43A, 1961, pp. 327-351. 



4. Chaffin, D. B., and W. H. Baker. 
Biomechanical Model for Analysis of Sym- 
metric Sagittal Plane Lifting. AIIE 
Trans., v. 2, Mar. 1970, pp. 16-27. 

5. Chaffin, D. B., and K. S. Park. A 
Longitudinal Study of Low Back Pain as 
Associated With Occupational Lifting Fac- 
tors. AM. Ind. Hyg. Assoc. J., v. 34, 
1973, pp. 513-525. 

6. Evans, F. G. , and H. R. Lissner. 
Biomechanical Studies on the Lumbar Spine 
and Pelvis. J. Bone Joint Surg. , v. 41A, 
1959, pp. 218-290. 

7. Garg, A., and D. B. Chaffin. A Bi- 
omechanical Computerized Simulation of 
Human Strength. AIIE Trans., v. 7, 1975, 
pp. 1-15. 



11. National Safety Council Accident 
Facts. Chicago, IL, 1975, pp. 23-37. 

12. Sonada, T. Studies on the Com- 
pression, Tension, and Torsion Strength 
of the Human Vertebral Column. J. Kyoto 
Prefect Med. Univ., v. 71, 1962, pp. 659- 
702. 

13. U.S. Department of Health and Hu- 
man Services Work Practices Guide for 
Manual Lifting. NIOSH Pub. 81-122, 1981, 
183 pp.; NTIS: PB 82-178-948. 

14. U.S. Mine Enforcement and Safety 
Administration. Injury Experience in the 
Nonmetallic Mineral Industries (Except 
Stone and Coal), 1970-71. MESA IR 1014, 
1975, 106 pp. 



45 



'abdomen-. 



e — *-, 



FmuscI 



■compression-TY /pg^g^' 



Center of gravity of body 
weight (BW) above 
lumbosacral joint 




Push or pul 
force 



Handle attached 
to 3-axis load 



FIGURE 1. . Free body diagram of the torso, showing variables used to calculate the c 



sive force at Lj-S ,. 



ompres- 



200 



150- 



_i 100- 



X 

a 

UJ 

5 




10 20 30 40 

HORIZONTAL LOCATION OF LOAD, In 

FIGURE 2, - Maximum weight versus horizontal 
location for infrequent lifts from floor-to-knuckle 
height (13), 



KEY 
V = 3in 
H = I8in 
D = 20in 
F = I lift per minute 




FIGURE 3, - Schematic representation of miner 
lifting material onto a cart. 



46 




Amplifier 

FIGURE 4, - Laboratory setup used to collect data 
for the biodynamic push-pull model. 



en 

Q 

< 
o 

_l 

LLl 

> 

CO 

(n 

UJ 

a: 
a. 

O 

o 



,000 



500 




KEY 
A= Push V, 32 In 
• = Pull V, 32 in 



20 40 60 80 

HAND FORCES, lb 



100 



120 



FIGURE 5. - Predicted L5-S, compressive 
forces (8). 




20 40 60 80 100 120 140 160 180 200 
TIME DURING STEP CYCLE, ms 



FIGURE 6. - Predicted required coefficient of fric- 
tion for one foot at the shoe-floor interface during a 
pushing task. 



47 



FIELD TESTING OF WORKERS INVOLVED IN MATERIAL HANDLING 
By Karl H. E. Kroemer' 



INTRODUCTION 



Many industrial jobs require the worker 
to manipulate objects, position loads, 
and perform other physical activities 
that are usually understood as "lifting." 
The physical efforts involved in lifting 
often overload the physical capability of 
the people performing them, leading to 
very large numbers of job-related inju- 
ries and to very high costs in terms of 
lost time, compensation payments, and re- 
training of new personnel. Thus, indus- 
try is trying to either select people ac- 
cording to their strength, to train them 
so that they are able to perform stress- 
ful jobs, or to limit the loads to be 
moved by workers so that they will not be 
overstressed. For screening, reliable 
and valid tests are needed that assess 
the capability of an individual to manip- 
ulate loads. Relatedly, job requirements 
must be known regarding the type and mag- 
nitude of loads to be manipulated. Both 
tasks are interrelated because job re- 
quirements should match the operator's 
capability to perform the jobs, and vice 
verse. 

Sponsored and coordinated by NIOSH, 
several researchers cooperated to deter- 
mine the conditions that would either 
constitute safe or hazardous lifting re- 
quirements. A summary of the research 
and recommendations derived from it were 
published in the 1981 NIOSH "Work Prac- 
tices Guide for Manual Lifting" (10).^ 



The guide utilizes weight to be lifted 
as the primary descriptor of the job re- 
quirements, but modifies this criterion 
by including the start and end points of 
the path of the lift, and by the frequen- 
cy of lifting. These job requirements 
then, ideally, are matched to capabili- 
ties of the operators, or vice versa. 
Operator capabilities can be established 
using physiological, psychophysical, and 
biomechanical response variables. Among 
biomechanical test procedures, until re- 
cently only static tests were at hand. 
While well established and tested, these 
procedures obviously do not represent the 
dynamic requirements of industrial lift- 
ing, where work is usually performed with 
body and object in motion. 

Psychophysical testing of a subject's 
dynamic capability for lifting was pre- 
viously developed in the laboratories 
of Liberty Mutual Insurance Co. and at 
Texas Tech University. NIOSH sponsored 
research for the development of an 
industrial dynamic testing technique 
at Virginia Polytechnic Institute and 
State University. This work resulted in 
a new testing procedure and technique, 
called LIFTEST. This dynamic technique 
promises to be more reliable than static 
strength testing and appears to be more 
indicative of a person's actual lifting 
capability. 



FITTING THE WORKER TO THE JOB VERSUS FITTING THE JOB TO THE WORKER 



Manual material handlings produces the 
single largest percentage of compensable 
work injury in U.S. industry, constitut- 
ing today one-fourth to one-third of all 

^Director, Ergonomics Research Insti- 
tute, Inc., Blacksburg, VA. 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



injuries. The cost to U.S. business is 
estimated" between $4 and $20 billion an- 
nually (_9, 10). Suffering of the injured 
and of their families cannot be expressed 
in dollar figures. 

-^This is often called lifting, although 
in its strict sense lifting refers exclu- 
sively to elevating an object from a low- 
er level to a higher one. 



48 



The following three major avenues exist 
to reduce the frequency and severity of 
these injuries: 

1. Screening of workers for their 
physical abilities to perform material 
handling. 

2. Training of workers to perform 
material handling in a manner that avoids 
accidents. 

3. Designing work task and work equip- 
ment so that workers will not be strained 
excessively by materials handling. 

This presentation concentrates on 
screening of workers for their physical 
capabilities to handle material at work 
without overexertion. 

After standard medical examinations 
were found ineffective for screening, 
more recently static muscular strength 
tests have been advocated (10). These 
assess isometric muscular strength of the 
human in discrete "frozen" body posi- 
tions, primarily by measuring leg force, 
back force, and arm force (2). In com- 
paring these scores via a biomechanical 
model of the human body with job require- 
ments, or injury data in general, it was 



found that isometrically "stronger" work- 
ers have fewer and/or less severe inju- 
ries than isometrically "weaker" workers 
(iO). 

The effectiveness of a screening tech- 
nique depends, to a large degree, on its 
ability to mimic the actual work require- 
ments that may overexert human capabili- 
ties. Static strength testing suffers in 
particular from the fact that it is done 
with the worker being immobile while ac- 
tual material handling usually involves 
motion. 

Because of the apparent deficiency in 
the validity of static testing, NIOSH 
sponsored research (under contract 210- 
79-0041) to develop a dynamic technique 
to test individual capability for lift- 
ing. This work resulted in a testing 
procedure, called LIFTEST, that was found 
to be highly reliable, as well as quick 
and simple to administer, in laboratory 
experiments (6^). While LIFTEST is ap- 
parently much more similar to actual 
material handling than static strength 
testing, its validity and effectiveness 
in screening workers for their capability 
to perform material handling tasks with- 
out injuries has yet to be assessed in a 
systematic manner. 



INDIVIDUAL CAPABILITIES SHOULD EXCEED JOB DEMANDS 



The premise of physical screening tech- 
niques is that human bodily capabilities 
will be measured and compared with re- 
lated job requirements; the more tested 
capabilities exceed job demands, the 
"safer" the person-job match. In mate- 
rial handling, many of the critical in- 
juries are related to the musculoskeletal 
system, particularly to the L5-S , region 
of the spinal column. As the guide for 
manual lifting indicates, there is an 



epidemiological relationship between in- 
dividual "strength" (as measured physio- 
logically, biomechanically , or psycho- 
physically) and job demands, with strong- 
er persons being less susceptible to 
injuries than their weaker cohorts. Even 
other injuries related to materials han- 
dling such as lesions, abrasions, etc., 
show correspondence with the strength 
criterion (10). 



ASSESSMENT OF INDIVIDUAL LIFT CAPABILITY 



Current static biomechanical models of 
the human performing material handling 
include anthropometry, isometric muscle 
force (or torque) capabilities, the abil- 
ity to withstand compression forces in 
the lower part of the lumbar spine, body 



posture descriptors, and work require- 
ments (J_). Unfortunately, the key in- 
gredient, isometric muscle strength capa- 
bility, is somewhat unrealistic because 
lifting and other material handling ac- 
tivities are performed with body and 



49 



load in motion and not in a static "fro- 
zen" condition. This discrepancy between 
static measurements and dynamic job re- 
quirements may explain why correlations 
between static strength and job perform- 
ance capabilities are usually unsatisfac- 
tory for predictive-preventive purposes, 
being in the neighborhood of only 0.5 

a). 

Researchers at the University of Michi- 
gan and at Texas Tech University devel- 
oped static muscle strength tests and re- 
lated their outcomes with incidences of 



physical overexertion in industries re- 
quiring material handling O, 8^). Both 
groups found that isometrically weaker 
persons suffered from a larger number of 
overexertion injuries than stronger sub- 
jects. However, some of the static 
strength tests showed practically no 
relationships to the probabilities of 
overexertion injuries. For example, of 
nine isometric strength tests applied by 
Keyserling (_5 ) , only four showed signifi- 
cant relations to the occurrences of mus- 
culoskeletal problems. 



LIFTEST 



Recognizing the problems of "unrealis- 
tic" static testing, NIOSH sponsored work 
to develop a dynamic testing procedure 
suitable for field application. This 
work was performed over a period of 2-yr, 
and resulted in the new technique called 
LIFTEST (6^). 

LIFTEST equipment consists essentially 
of a carriage that a person moves up and 
down within vertical guardrails. Varia- 
ble weights are attached to the rear part 
of the carriage in such a manner that the 
subject is unable to see them. The per- 
son grasps the handles protruding from 
the carriage near floor height and lifts 
them, with carriage and weights attached, 
to her or his individual overhead reach 
height. Using a suitable sequence, the 
maximum weight that the individual can 
lift to overhead reach is determined 
within 2 or 3 min. In test-retest relia- 
bility experiments performed in the lab- 
oratory, 39 subjects could lift, on the 
average, 59.3 lb to overhead reach, with 
a standard deviation of 22.7 lb. This 
range indicates that the strength capa- 
bilities of the subjects employed were 
rather different. However, the subjects, 
whether weak or strong, showed a con- 
sistent low intra-individual variabil- 
ity of their individual scores in repeat- 
ed tests. The average coefficient of 
variation was only 3.5 pet, compared 
with 13 pet in isometric strength tests 
(6). In rather similar "Factor X" tests 
with almost 600 subjects, male and fe- 
male, the U.S. Air Force also found that 



such dynamic lift tests are much more 
reliable (i.e. , less variable in repeat- 
ed tests) than isometric muscle strength 
measurements. 4 Relatedly, isokinetic 
(i.e., constant speed) strength testing 
also showed relatively low correlations 
with isometric muscle strength testing 
(4^). This strongly supports the notion 
that the dynamic LIFTEST can be used re- 
liably to assess lift capability. What 
was not measured (and not intended to be 
measured) in the NIOSH-sponsored labor- 
atory research was the validity of the 
test, that is, its relationship to actual 
lifting performance in industry. While 
having obvious "face-validity," the prac- 
tical effectiveness of the LIFTEST pro- 
cedure needs to be established in field 
tests. Interestingly enough, the U.S. 
Air Force used simulated "actual" lift 
tasks to validate their dynamic "Factor 
X" testing. The correlation between lift 
test results, and actual lift performance 
was about 0.9.5 a correlation of 0.75 
between isokinetic and actual lifting 
capability has been reported (4^) . These 
results strongly support the expectation 
that the LIFTEST procedure will be an ef- 
ficient predictor of lifting capability 
on the job. 

According to the premise discussed 
above, the ratio "strength available to 
strength required" would indicate the 



'^McDaniel, J. W. Personal Communica- 
tion, Jan. 24, 1983. 
^See footnote 4. 



50 



probability of an overexertion injury; 
a high ratio would make this probabil- 
ity small, a ratio close to unity would 
indicate a high probability. Used as 
a screening technique, one would avoid 
placing persons with a low ratio in jobs 
requiring such strength exertion, or 



reduce job requirements by administra- 
tive or engineering intervention. Per- 
sons with a high ratio could be employed 
in jobs requiring manual material han- 
dling with little danger of overexertion 
injuries. 



ASSESSMENT OF JOB LIFTING REQUIREMENTS 



The NIOSH guide provides a standardized 
procedure to assess the job requirements 
involved in material lifting tasks. The 
guide ( 10 , p. 124) establishes three 
major categories of hazards in material 
handling. They are divided by the so- 
called "action limit" and the "maximum 
permissible limit." Below the action 
limit, no hazard to the individual is ex- 
pected that would require engineering 
or administrative interaction. A "gray" 
zone exists between the action lim- 
it and the maximum permissible limit 
where suitable intervention methods 
are needed. These might mean worker 
screening-selection methods, and/or might 
involve engineering measures to reduce 
the worker's lift effort. Requirements 
above the maximum permissible limit are 
unacceptable. 

The guide sets the maximum permissible 
limit numerically to be three times larg- 
er than the action limit. It appears 
reasonable to divide this zone between 
action and maximum permissible limits in- 
to two zones by doubling the action limit 
values. Hence, work requirements that 
fall below the doubled action limit would 
be less hazardous than those conditions 
falling between twice the action limit 



and maximum permissible limit values. 
Using such subdivision, one can cate- 
gorize job demands in the following 
four areas: below action limit, between 
single- and double-action limit, between 
double-action limit and maximum permissi- 
ble limit, and above maximum permissible 
limit. 

According to the guide ( 10 , p. 126) , 
the following job variables primarily 
determine the job requirements: the ini- 
tial starting point of the load, the 
end point of the lifting path, and the 
frequency of lifts per time unit per- 
formed. The individual contributions of 
these variables are expressed by an alge- 
braic formula in the guide ( 10 , p. 126). 
Start and end point are described by the 
height above the floor upon which the 
worker stands, and by the vertical dis- 
tance away from the body of the worker. 
The frequency of lift is compared with a 
maximum frequency deemed suitable. The 
numerical values for these parameters are 
inserted into the formula given in the 
guide. Furthermore, the guide describes 
a measurement technique to determine the 
actual lift requirements at any given 
workplace. 



COMPARING WORKER CAPABILITIES TO JOB REQUIREMENTS 



Whereas the NIOSH guide provides a 
standard approach to establish job re- 
quirements, the LIFTEST procedure pro- 
vides an equally convenient method to de- 
termine related physical capabilities of 
the worker. The LIFTEST regimen provides 
for a minimum load of 25 lb, and a maxi- 
mum load of 100 lb to be employed for the 
establishment of overhead capability 
scores. With test weight increments of 5 
lbs used, 18 different lift scores can be 
obtained, ranging from below 25 lb, at 25 



lb increasing in steps of 5 lb to 100 lb, 
to exceeding 100 lb. (The 5-lb increment 
values can be combined to larger units, 
such as 10 lb, in order 
number of lift capability 
convenient. ) 



to reduce the 
assessments as 



In summary, the guide provides a stan- 
dardized procedure to assess lift re- 
quirements imposed by the job. LIFTEST 
provides a reliable procedure to assess 
dynamic individual lift capabilities. 



51 



LIFTEST PROCEDURE FIELD STUDIES 



The general aim of a field study being 
organized by the author is to assess the 
effectiveness of the LIFTEST procedure as 
a screening technique for reducing sever- 
ity and frequency of overexertion inju- 
ries resulting from manual material move- 
ment, particularly lifting. 

The specific aims of this study are 



2. Monitor overexertion and other re- 
lated injury events of these workers over 
a 3-yr period. 



3. Determine 
needed. 



job lift strains, 



4. Compare injury statistics with per- 
formance in LIFTESTs. 



1. Measure individual lifting capabil- 
ities, via the LIFTEST procedure, approx- 
imately 15,000 workers doing material 
handling. 



5. Assess the effectiveness of the 
LIFTEST procedure as a screening tech- 
nique based on the results of aims 1 
through 4. 



METHODS 



Several large industries in Virginia, 
North Carolina, and Tennessee have con- 
sented to participate in this study. 
Others are invited to participate. 

The currently participating industries 
employ about 50,000 hourly paid persons. 
Of these workers, approximately 30 pet 
have jobs that include material handling. 
If these 15,000 workers have a related 
accident-injury rate during the 3-yr re- 
search period of approximately 10 pet 
(5, 10), approximately 1,500 cases would 
be present. Even if a dropout rate of 
one-third (which would be very high in- 
deed) existed in the subject population, 
approximately 1,000 cases present in the 
study would constitute a solid statisti- 
cal basis. 

In order to establish the effectivenss 
of the LIFTEST procedure, the following 
steps will be taken: 

1 . Measure individual lifting capabil- 
ities of approximately 15,000 workers 
involved in material handling . The co- 
operating industries will identify, in- 
ternally, in accordance with existing 
management-labor practices and agree- 
ments, jobs with material handling re- 
quirements and the persons either incum- 
bent in the jobs, being transferred to 
them, or to be hired for them. These 
persons will be measured, usually in con- 
junction with a routine physical examina- 
tion, in their LIFTEST performance by the 
companies' medical staff. In order to 



ensure uniformness and consistency in the 
application of the LIFTEST procedure, the 
initial equipment setup and training of 
the staff applying the tests will be pro- 
vided by the author and his team. 

Test results will become part of the 
medical record kept by the industries in 
accordance with their existing safeguard- 
ing practices. 

2. Monitor over exe rtion and other re- 
lated injuries of workers over a 3-yr 
period. Participating industries will 
monitor injuries related to material han- 
dling according to the industry-estab- 
lished practices. This assures that ano- 
nymity and privacy of the worker rec- 
ords remain intact, such as they would be 
without this investigation. 

3. Determine job lift requirements. 
The author and his team will, in coopera- 
tion with industry personnel, and in ac- 
cordance with local management-labor 
practices, determine the actual lifting 
requirements of jobs that have a poten- 
tial for, or a record of, lifting-related 
overexertions. This will be done accord- 
ing to reference 10. 

The assessment of job requirements will 
be independent from the person actually 
occupying the job. Hence, personal rec- 
ords of the worker will not be provided 
to the investigators but will remain in 
custody of the industry. 



52 



4. Compare Injury statistics with 
LIFTEST performance . The participating 
companies will compare accident severity 
and frequency, according to ANSI and OSHA 
standards, with performance on LIFTEST. 
Where the accident circumstances are not 
obvious, the industry will cooperate with 
the investigators in the determination of 
job requirements prevailing at the injury 
time (step 3). With the four categories 
of NIOSH-def ined job requirements and 18 
LIFTEST procedure-performance steps, in- 
cidents can be recorded on a 4 by 18 
matrix. (If required, the NIOSH job re- 
quirement categories can be further sub- 
divided and/or the number of LIFTEST 
performance score categories be reduced, 
as described above.). Only anonymous 
information regarding incidence and test 
performance will be received by the 
investigators. 



Establish 



effectiveness of the 



LIFTEST procedure as a screening tech- 
nique . Based on the data collected in 
steps 1 through 4, correlations between 
LIFTEST performance and injuries will be 
established. In a first step, LIFTEST 
performance will be compared with injury 
severity and frequency, following common 
practice in industrial and injury statis- 
tics. In this case, the actual job re- 
quirements are not considered in detail. 
As a second step, detailed comparison of 
job requirements with LIFTEST performance 
will be done, based on the results of the 
specific job requirement assessments. 
This will identify correlations between 
general and specific job requirements 
(such as lift frequency, initial position 
of the load, final position of the load, 
etc.) and LIFTEST performance. 



STATISTICS 



The statistical procedures are simple 
and straightforward, using the industry- 
common ANSI Z16 technique. This facili- 
tates the cooperation with industry. 



and 



Oj = observed number of inci- 
dents in category i, 

i=l, 2, 3, ...m. 



As in previous experiments (_5) , the 
following chi-square formula to test the 
significance of differences between inci- 
dent rates and test performance will also 
be used. 



The values of Ej are computed with the 
following equation: 



E, =|t^«r. 



(2) 



2 = ? (Ej - Qj)^ 



Xm-1 



i=l E, 



(1) 



where Xm-1 = test statistic with (m-1) 
degree of freedom, 

m = number of LIFTEST score 
categories being 
compared. 



where H| = hours of exposure in 
category i, 

H^ = total hours of exposure 
across all categories, 

or 0^ = total number of observed 
incidents across all 
categories. 



Ej = expected number of inci- 
dents in category i, 
based on exposure, 



CONCLUSION 



53 



While the basic solution is to design 
jobs to fit the worker, training and, in 
particular, selection of individuals for 
safe material handling are also indispen- 
sable. Regarding screening, the testing 
should be "realistic," that is, represent 



actual job demands. Dynamic tests appear 
to be more suitable than static muscle 
strength testing. Procedures to develop 
and apply such dynamic testing are at 
hand. 



REFERENCES 



1. Ayoub, M. M. , A. Mital, S. S. 
Asfour, and N. J. Bethea. Review, Evalu- 
ation, and Comparison of Models for Pre- 
dicting Lifting Capacity. Human Factors, 
v. 22, No. 3, 1980, pp. 257-269. 

2. Chaffin, D. B. Functional Assess- 
ment for Heavy Physical Labor. Occupa- 
tional Health and Safety, v. 50, No. 1, 
1981, pp. 24, 27, 32, 64. 

3. Chaffin, D. B. , G. D. Herrin, W. M. 
Keyserling, and J. A. Foulke. Pre- 
Employment Strength Testing in Selecting 
Workers for Materials Handling Jobs. 
DHEW Rept. 77-163, 188 pp.; NTIS PB- 
298-677. 

4. Kamon, E., D. Kiser, and J. L. 
Pytel. Dynamic and Static Lifting Capac- 
ity and Muscular Strength of Steelmill 
Workers. Am. Ind. Hyg. Assoc. J. , v. 43, 
No. 11, 1982, pp. 853-857. 

5. Keyserling, W. M. , G. D. Herrin, 
D. B. Chaffin, T. J. Armstrong, and 
M. L. Foss. Establishing an Industrial 
Strength Testing Program. Am. Ind. Hyg. 
Assoc. J., V. 41, No. 10, 1980, pp. 730- 
736. 

6. Kroemer, K. H. E. Development of 
"LIFTEST," A Dynamic Technique to Assess 



the Individual Capability to Lift Materi- 
al. Final Report, NIOSH contract 210- 
79-0041. Ergonomics Laboratory, VA Poly- 
technic Inst, and State Univ. , Febru- 
ary 26, 1982, available upon request from 
K. H. E. Kroemer, Ergonomics Research In- 
stitute, Blacksburg, VA. 

7. Mital, A., and M. M. Ayoub. Model- 
ing of Isometric Strength and Lifting 
Capacity. Human Factors, v. 22, No. 3, 

1980, pp. 285-290. 

8. Mital, A., M. M. Ayoub, S. S. 
Asfour, and J. J. Bethea. Relationship 
Between Lifting Capacity and Injury 
in Occupations Requiring Lifting. Paper 
in Proceedings, Annual Meeting of the 
Human Factors Society (Detroit, MI, 
Oct. 16-19, 1978). Santa Monica, CA, 
pp. 469-473. 

9. Nordby, E. J. Epidemiology and 
Diagnosis in Low Back Injury. Occupa- 
tional Health and Safety, v. 50, No. 1, 

1981, pp. 38-42. 

10. U.S. Department of Health and Hu- 
man Services. Work Practices Guide for 
Manual Lifting. NIOSH Pub. 81-122, 183 
pp.; NTIS PB 82-178-948. 



54 



LIFTING CAPACITY DETERMINATION 
By M. M. Ayoub.l J. L. Selan,2 w. Karwowski,3 and H. P. R. Rao4 



ABSTRACT 



Given the large number of tasks in the 
mining industry that require manual mate- 
rials handling (MMH) and the enormous 
costs associated with musculoskeletal in- 
juries resulting from MMH, job design and 
employee placement procedures for MMH 
tasks in the mining industry would be 
beneficial. A major step in establishing 
these procedures is the determination of 
the lifting capacity of the individual or 
population performing a given lifting 
task. The three primary approaches used 
to determine lifting capacity are the bi- 
omechanical approach, the physiological 



approach, and the psychophysical ap- 
proach. This paper proposes the use of 
the psychophysical approach to determine 
lifting capacity owing to the fact that 
it attempts to combine the biomechanical 
and physiological stresses present in all 
lifting tasks under a measure of per- 
ceived stress. A mathematical, fuzzy- 
sets-based model of lifting capacity is 
presented that demonstrates that the com- 
bining of acceptability measure for psy- 
chophysical stress. Advantages of the 
fuzzy-sets-based model and examples of 
its use are given. 



INTRODUCTION 



Manual materials handling (MMH) activi- 
ties, and in particular manual lifting, 
are recognized as a major hazard to the 
safety and health of industrial workers 
(17)5 and a majorcost to industry (10). 
Recent evidence ( 19 ) supports the notion 
that numerous tasks in the mining indus- 
try involve manual lifting, and as such 
could be helped by improved job design 
and employee placement procedures in or- 
der that job demands can be controlled to 
stay within individual capacities. A 
major step in the establishment of such 
procedures is the determination of the 



lifting capacity of the individual or 
population performing these jobs. It has 
been noted by Karwowski ( 11 ) that no OSHA 
regulations exist regarding the maximum 
acceptable weight of lift; this being 
due in part to the fact that existing 
recoimnendations are based on different 
methodological approaches assessing dif- 
ferent categories of stresses in MMH ac- 
tivities. The three primary approaches 
to determine lifting capacity are (1) the 
biomechanical approach, (2) the physio- 
logical approach, and (3) the psychophys- 
ical approach. 



BIOMECHANICAL APPROACH 



In general, biomechanics determines 
what a person can physically do. Bio- 
mechanical models attempt to establish 
the physical stresses imposed on the 
musculoskeletal system during a lifting 
action; these stresses serve as the 

^Horn professor of industrial and bio- 
medical engineering, Texas Tech Univer- 
sity, Department of Industrial Engineer- 
ing, Lubbock, TX. 

^Research associate, Texas Tech Univer- 
sity, Department of Industrial Engineer- 
ing, Lubbock, TX. 



criteria upon which capacity of lift 
is based. These physical stresses in- 
clude reaction forces and torques on var- 
ious joints of the body (4^) and compres- 
sive and shear forces on the lower back 

■^Assistant professor, Iowa State Uni- 
versity, Ames, lA. 

"^Research associate, Texas Tech Univer- 
sity, Department of Industrial Engineer- 
ing, Lubbock, TX. 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



55 



_5-^). The low back, in particular the 
L4-L5 and L5-S, disks of the lower back, 
is especially considered as a basis for 
load lifting limits owing to the exces- 
sively high forces produced on the low 
back when lifting O, _18, 22^) and the 
large number of back injuries arising 
from manual lifting. 

The ultimate goal of the biomechanical 
approach is to set limits on these physi- 
cal stresses imposed during lifting and 
then determine the load-lifting capacity 
based on these limits. Towards this 
goal, both static and dynamic models of 
lifting capacity have been developed 
based on the biomechanical approach. 
Static biomechanical models, such as 
those developed by Chaff in ( 4_) , assume 
that the lifting action is performed 
slowly and smoothly such that forces due 
to the acceleration can be neglected. 
Dynamic models, such as those developed 
by Fischer (7), El-Bassoussi (6), Ayoub 
O), and Muth ( 16 , pp. 96-109), provide 
data for analyses in the form of time- 
displacement relationships of the body 
segments (kinematic analysis) and the 
forces and torques involved in the motion 
(kinetic analysis). 

Figure 1, based on the dynamic biome- 
chanical model developed by El-Bassoussi 
(6) and Ayoub (3), presents lifting ca- 
pacity guidelines developed using the 
biomechanical approach. The figure shows 
three different lifting regions based on 
compression on the spine. Weights of 



lift producing con^ressive forces of less 
than 1,100 lb are considered acceptable 
(i.e., minimal risk of injury to worker). 
Lifting tasks producing compressive 
forces of 1,540 lb or more are considered 
hazardous and should be redesigned. The 
region between these two values falls un- 
der the area of administrative control. 
As is also indicated in the figure, if 
the center of gravity (CG) of a load from 
the spine is 20 in, an acceptable weight 
of load would be 25 lb, and a weight of 
load of 69 lb or more would produce ex- 
cessive compressive forces on the spine. 
The constant compression lines were de- 
veloped using the concept of a biomechan- 
ical equivalent (22) in the form of 



BE = H 



(w). 



where BE = biomechanical equivalent, 
pound-inch, 

H = horizontal distance of the 
CG of the load from the 
spine, inches. 



and 



W = weight of the load, pounds. 



The model allows the calculation of the 
compressive and shearing forces on the 
Lc-S^ disk during the time course of a 
lifting movement in the sagittal plane 
from floor to a 2.5-ft height. The out- 
put of the model include the reactive 
forces and torques at several joints in- 
volved in the motion. 



PHYSIOLOGICAL APPROACH 



The physiological approach may use sev- 
eral criteria, such as oxygen consump- 
tion, heart rate, pulmonary ventilation 
volume, or percent of physical work ca- 
pacity, as indices of heaviness of work 
performed. Generally, the criterion used 
is the energy expenditure while lifting 
loads. 

Oxygen consumption is generally mea- 
sured to estimate the energy expenditure 
required by a lifting task. The measure- 
ment of the physiological demands can al- 
so be related to an individual's maximum 
aerobic capacity in order to determine 



what percent of that capacity a given 
lifting task requires. 

As with the biomechanical approach, the 
goal of the physiological approach is to 
develop limits using metabolic energy ex- 
penditure criteria and then determine 
lifting capacity based on the chosen cri- 
teria limits. Several prediction models 
of metabolic energy expenditure for lift- 
ing tasks have been developed (4^, 8^-^). 
Based on the physiological approach, 
it has been concluded that, for a young 
male, the 8-h average metabolic rate 
should not exceed 5 kcal/min or 33 pet of 



56 



the individual's maximum aerobic capac- 
ity, and heart rate should not exceed 110 
to 115 beats per minute (20). Figure 2, 
based on the model reported by Garg ( 11 ) , 
shows the effect of frequency of lift 



(lifts per minute) and lifting technique 
on the weight of load that can be lifted 
to maintain an energy expenditure of 5 
kcal/min. 



PSYCHOPHYSICAL APPROACH 



The third method employed to determine 
lifting capacity is the psychophysical 
approach. Psychophysics deals with the 
relationship between human sensations and 
their physical stimuli; this relationship 
best being described by a power function 
(21). The use of psychophysics in lift- 
ing tasks requires the subject to adjust 
the weight of load according to his or 
her own perception of effort such that 
the lifting task does not result in over- 
exertion or excessive fatigue. The final 
weight decided upon by the subject repre- 
sents the maximum acceptable weight of 
lift for the given job conditions (fre- 
quency of lift, height of lift, container 
size, etc.). 

Several lifting capacity prediction 
models using the psychophysical approach 
have been developed (13-15). The major 
limitation with these models has been 
that they are applicable to only one or 
two lifting ranges and only one frequency 
of lift. Ayoub (2) developed lifting 



capacity prediction models that were more 
flexible than the previously developed 
models in that six ranges of lift and 
different work paces were accommodated by 
the model. Table 1 presents the lifting 
capacity norms for male and female indus- 
trial workers developed by Ayoub (2). 
Figure 3 presents capacity norms adjusted 
for load size and frequency of lift de- 
veloped by the senior author. The capac- 
ity norms are given by the formula 

LC = rv X a X b, 

where LC = capacity of lift, pounds, 

rv = reference value at one lift 
per minute, 

a = percent multiplier for 
frequency, 

and b = percent multiplier for load 
size 



TABLE 1. - Distribution of maximum weights of lift acceptable to male 
and female industrial workers' (corrected for one lift per minute 
and load size of 18 in), pounds 



Range of lift 


Sex 


Mean 


SD 




Percent 


of population 






95 


75 


50 


25 


5 


Floor to knuckle 


Male... 
Female. 


61.17 
37.12 


16.87 
6.76 


33.43 
26.00 


49.62 
32.50 


61.17 
37.12 


72.71 
41.73 


88.90 




48.20 


Floor to shoulder 


Male... 


51.12 


12.11 


31.29 


42.91 


51.21 


59.50 


71.13 




Female. 


31.08 


6.54 


20.32 


26.60 


31.08 


35.56 


41.83 


Floor to reach 


Male. . . 
Female. 


49.12 
28.14 


11.20 
5.41 


30.69 
19.24 


41.45 
24.41 


49.12 
28.14 


56.79 
31.84 


67.54 




37.04 


Knuckle to shoulder 


Male... 


57.75 


14.67 


33.33 


47.42 


57.47 


67.52 


81.60 




Female. 


31.97 


6.55 


21.19 


27.48 


31.97 


36.45 


42.74 


Knuckle to reach 


Male. . . 
Female. 


53.54 
26.22 


10.70 
4.86 


35.93 
18.22 


46.21 
22.89 


53.54 
26.22 


60.87 
29.55 


71.14 




34.21 


Shoulder to reach. ......... 


Male. . . 
Female. 


43.62 
25.78 


10.45 
4.17 


26.43 
18.92 


36.46 
22.92 


42.62 
25.78 


50.77 
28.63 


60.81 




32.64 


SD Standard deviation. 'As 


suminp a 


normal 


distrit- 


Kitlon. 











57 



COMPARISON OF THE THREE APPROACHES 



It is the assertion of this paper that 
the psychophysical approach is the appro- 
priate single approach to use to deter- 
mine lifting capacity. The problem with 
the use of the biomechanical approach or 
the physiological approach alone is that 
both biomechanical and physiological 
stresses are usually present in almost 
all lifting tasks. Using the aforemen- 
tioned physiologically based guidelines 
proposed by Snook (20) , it is intuitively 
obvious that an individual could stay 
within the recommended physiological lim- 
its by lifting a very heavy load at a low 
frequency of lift. However, such a pro- 
cedure would violate lifting capacity 
recommendations based on biomechanical 
criteria. Conversely, lifting capacity 
models based solely on biomechanical cri- 
teria are wholly inadequate in dealing 
with the effects of repetitive lifting on 
the cumulative physical stresses imposed 
on the body. 

The discrepancies encountered by the 
use of biomechanical or physiological 
criteria alone in the determination of 
lifting capacity become evident when com- 
paring the lifting guidelines presented 
in figure 1 (using the biomechanical ap- 
proach) and the lifting guidelines pre- 
sented in figure 2 (using the physiologi- 
cal approach). Although attempting to 
make comparisons between these two ap- 
proaches is difficult, the aforementioned 
problems associated with using only a 
biomechanical or physiological criterion 
can be made more evident. For example, 
a weight of load of 88.2 lb is acceptable 
at low frequencies of lift using the 



physiological approach, whereas this same 
weight of load significantly exceeds the 
acceptable lifting region recommended 
when using the biomechanical approach. 
In fact, in situations where the horizon- 
tal distance of the center of gravity of 
the load from the spine exceeds approxi- 
mately 12 in, a weight of load of 88.2 lb 
is considered hazardous based on the bio- 
mechanical criteria. 

In general MMH recommendations based on 
biomechanical models suggest lifting 
light loads at higher frequencies of 
lift, whereas physiological models sug- 
gest the lifting of heavier loads at a 
reduced frequency of lift. Also, it is 
often assumed by researcher in the area 
of MMH that only biomechanical criteria 
need to be considered if the frequency of 
lift is low, and only physiological cri- 
teria need to be considered for higher 
frequencies of lift. This could be a 
dangerous oversimplification. 

Lifting is a task of a complex nature 
such that it cannot be fully explained 
using only physiological or biomechani- 
cal criteria. Both physiological and 
biomechanical stresses, among others, 
are present in every lifting task and, 
as such, the need exists for a means of 
determining lifting capacity that can 
accommodate both of these everpresent 
stresses. The virtue of the psycho- 
physical approach is that it attempts to 
combine the stresses, including the bio- 
mechanical and physiological stresses 
present in the lifting task under a mea- 
sure of perceived stress. 



COMBINED STRESS VERSUS PSYCHOPHYSICAL STRESS 



The psychophysical approach is based on 
the assumption that the biomechanical and 
physiological stresses are integrated or 
combined under the measure of perceived 
stress. No theoretical method has exist- 
ed in the past for combining the biome- 
chanical and physiological stresses to 
determine their relationship with the 
psycholphysical stress. However, a re- 
cent model of lifting capacity developed 



and reported by Karwowski (11-12) has 
provided a means by which the relation- 
ship between the combined effects of bio- 
mechanical and physiological stresses and 
the perceived stress determined psycho- 
physically can be explained. 

Karwowski ( 11 ) hypothesized that a 
combination of the acceptability of bio- 
mechanical and physiological stresses 



58 



imposed during manual lifting leads to an 
overall measure of the lifting task ac- 
ceptability, expressed by the acceptabil- 
ity of the psychophysical stress. Toward 
the testing of this hypothesis, Karwowski 
utilized a fuzzy sets theory [for a thor- 
ough explanation of the concept and fun- 
damentals of fuzzy sets theory refer to 
Zadeh (23)]. 

Karwowski (11) developed a fuzzy set 
model from which an acceptability measure 
for biomechanical stress and an accepta- 
bility measure for physiological stress 
could be integrated into a measure of 
combined stress. Following this, mathe- 
matical procedures stemming from fuzzy 
sets theory were used to determine the 
relationship between the maximum accepta- 
ble weight of lift from the psychophysi- 
cal and combined standpoints. Based on 
these mathematical procedures, Karwowski 
(11) concluded that the maximum accepta- 
ble weight of lift based on a psychophys- 
ical criterion appears to be the result 
of the integration of the biomechanical 
and physiological stresses imposed by the 
lifting task. 

Figure 4 shows the relationship between 
the acceptability measures of the com- 
bined stress versus the acceptability 
measures of the psychophysical stress. 
The combined stress is determined by tak- 
ing the algebraic product of the accepta- 
bility measures of the biomechanical and 
physiological stress. The acceptability 
measure is determined using membership 
functions developed by Karwowski (11) for 
the biomechanical, physiological, and 
psychophysical stress. The degree of 
membership can be any value ranging from 
to 1 , with representing nonmembership 
in a set, and 1 indicating total member- 
ship in the set. The stresses given a 
value of 1 (i.e., are totally acceptable 
in terms of stress imposed) .were selected 
based on past research in the areas of 
acceptable biomechanical, physiological, 
and psychophysical stresses. For exam- 
ple, the membership function for the ac- 
ceptability of the psychophysical stress 
was based on the lifting capacity norms 
presented in figure 1. 



One of the advantages presented by the 
fuzzy-sets-based model is that it allows 
for the determination of lifting capaci- 
ty, and consequently allows for the de- 
sign of a lifting task, without the ne- 
cessity of performing any psychophysical 
experiments. By determining the accepta- 
bility measure of the biomechanical and 
physiological stresses imposed on the in- 
dividual while lifting a specified weight 
of load and then combining these two 
stresses into a single category, the lev- 
el of psychophysical stress that is like- 
ly to occur for this particular lifting 
task can be assessed. In addition, pre- 
dictive models already exist whereby the 
physiological and biomechanical stresses 
can be determined without extensive ex- 
perimentation. Oxygen consumption can be 
predicted using equations such as those 
developed by Garg (9) or Asfour (J^) . Bi- 
omechanical stresses can be predicted us- 
ing a dynamic biomechanical model such as 
the one developed by El-Bassoussi (6^). 

Using an example from Karwowski (11), 
consider a task in which an individual 
lifts 75 lb from floor to knuckle height 
at a frequency of three lifts per minutes 
using a squat lifting technique (i.e., 
back straight, bent at knees). Given 
these task conditions, oxygen consumption 
would be approximately 0.886 L/min and ] 
the biomechanical stress imposed would be 
1,690 lb, with the acceptability measures 
for the physiological and biomechanical 
stress based on the fuzzy sets model be- 
ing 0.7929 and 0.5233, respectively. The 
membership functions for the biomechani- 
cal and physiological stress from which 
the acceptability measures were deter- 
mined are given in figures 5 and 6, re- 
spectively. The combined stress is then 
determined to be 0.4150 (by taking the 
algebraic product of the acceptability 
measures of the biomechanical and physio- 
logical stress). The hypothetical capac- 
ity norm can then be determined by multi- 
plying the 75 lb by the acceptability 
measure for the combined stress. Based 
on this product , it can be concluded that 
a weight of load of 31.13 lb would repre- 
sent a totally acceptable weight for the 
given task. 



59 



To further illustrate the relationship 
between the acceptability measures for 
the combined stress and the psychophysi- 
cal stress, the psychophysical stress 
calculated by the fuzzy sets model was 
0.4552. As can be seen in figure 7, the 
capacity norm based on the psychophysical 
methodology is 34.14 lb. The difference 



between this norm and the hypothetical 
capacity norm derived from the combined 
stress is 3.01 lb (9.13 pet). This rep- 
resents more evidence that the psycho- 
physical stress is a combination of the 
physiological and biomechanical stresses 
imposed on the individual while lifting. 



SUMMARY 



Figure 8 presents a model of lifting 
performance that summarizes the proposals 
made in this paper. First, the ultimate 
goal and purpose of lifting capacity de- 
termination is to stay within individual 
capacity when designing total job demand. 
By accomplishing this , the percentage of 
the population able to perform the task 
increases and the injuries associated 



with people exceeding or approaching 
their physical capabilities diminishes. 
Second, in order to match individual ca- 
pacity with total job demand, the lifting 
capacity of workers must be determined. 
This paper hopefully has proposed that 
the psychophysically determined lifting 
capacity should be used as the basis for 
job design and placement of workers. 



REFERENCES 



1. Asfour, S. S. Energy Cost Predict- 
ing Models for Manual Lifting and Lower- 
ing Tasks. Ph.D. Dissertation, Texas 
Tech University, Lubbock, TX, 1980. 

2. Ayoub, M. M. , N. J. Bethea, S. 
Deivanayagam, S. S. Asfour, and M. 
Sherif. Determination and Modeling of 
Lifting Capacity. Final Rept. HEW 
(NIOSH) grant No. 5R010H-00545-02, Sep- 
tember 1978; available upon request from 
M. M. Ayoub, Texas Tech Univ., Lubbock, 
TX. 

3. Ayoub, M. M. , and M. M. El- 
Bassoussi. Dynamic Biomechanical Model 
for Sagittal Lifting Activities. Paper 
in Proceedings of the 6th Congress of In- 
ternational Ergonomics Association, 1976, 
pp. 355-359. 



Medical Publishers, Inc., Chicago, IL, 
1975, Chapter 19. 

6. El-Bassoussi, M. M. A Biomechani- 
cal Dynamic Model for Lifting in the 
Sagittal Plane. Ph.D. Dissertation, Tex- 
as Tech University, Lubbock, TX, 1974; 
available upon request from M. M. Ayoub, 
Texas Tech Univ., Lubbock, TX. 

7. Fisher, B. 0. Analysis of Spinal 
Stresses during Lifting. Unpublished 
M.S. Thesis, The University of Michigan, 
Ann Arbor, MI, 1967; available upon re- 
quest from M. M. Ayoub, Texas Tech Univ., 
Lubbock, TX. 



8. Frederik, 
Manual Lifting, 
dling, V. 14, No, 



W. S. Human Energy in 
Modern Materials Han- 
3, 1959, pp. 74-76. 



4. Chaffin, D. B. The Development of 
a Prediction Model for Metabolic Energy 
Expended During Arm Activities. Unpub- 
lished Ph.D. Dissertation, University of 
Michigan, 1967; available upon request 
from M. M. Ayoub, Texas Tech Univ., Lub- 
bock, TX. 

5. Chaffin, D. B. Manual Materials 
Handling and Low Back Pain. Occupational 
Medicine, Principles and Practical Ap- 
plications. Ed. by C. Zenz Year Book 



9. Garg, A. A Metabolic Prediction 
Model for Manual Materials Handling Jobs. 
Unpublished Ph.D. Dissertation, The Uni- 
versity of Michigan, Ann Arbor, MI, 1976; 
available upon request from M. M. Ayoub, 
Texas Tech Univ., Lubbock, TX. 

10. Goldberg, H. M. Diagnosis and 
Management of Low Back Pain. J. of Occu- 
pational Health and Safety, v. 49, No. 6, 
June 1980. 



60 



11. Karwowski, W. A Fuzzy Sets Based 
Model on the Interaction Between Stresses 
Involved in Manual Lifting Tasks. Unpub- 
lished Ph.D. Dissertation, Texas Tech 
University, Lubbock, TX, 1982; available 
upon request from M. M. Ayoub, Texas Tech 
Univ. , Lubbock, TX. 

12. Karwowski, W. , and M. M. Ayoub. 
Fuzzy Approach in Psychophysical Modeling 
of Human Operator-Manual Lifting System. 
Unpublished article, January 1983; avail- 
able upon request from M. M. Ayoub, Texas 
Tech Univ., Lubbock, TX. 

13. Knipfer, R. E. Predictive Models 
for the Maximum Acceptable Weight of 
Lift. Ph.D. Dissertation, Texas Tech 
University, Lubbock, TX, 1974. 

14. McConville, J. T. , and H. T. E. A. 
Hertzberg. A Study of One Hand Lifting: 
Final Report. Wright-Patterson AFB, OH, 
Aerospace Med. Res. Lab., Tech. Rept. 
AMRL-TR-66-17, May 1966. 

15. McDaniel, J. W. Prediction of Ac- 
ceptable Lift Capability. Ph.D. Disser- 
tation, Texas Tech University, Lubbock, 
TX, 1972. 

16. Muth, M. B., M. M. Ayoub, and 
W. A. Gruver. A Nonlinear Programming 
Model for the Design and Evaluation of 
Lifting Tasks. Chapter in Safety in 



Manuals Materials Handling, ed. by Colin 
G. Drury, NIOSH, Pub. 78-185, 1978, 219 
pp.; NTIS PB-297-660. 

17. National Safety Council. Accident 
Facts. Chicago, IL. , 1981. 

18. Park, K. S., and D. B. Chaffin. A 
Biomechanical Evaluation of Two Methods 
of Manual Load Lifting. Trans. AIIE, 
V. 6, 1974, pp. 105-113. 

19. Selan, J., M. M. Ayoub, and 
H. P. R. Rao. Manual Materials Handling 
in the Mining Industry. Unpublished re- 
port; available upon request from M. M. 
Ayoub, Texas Tech Univ. , Lubbock, TX. 

20. Snook, S. H. , and C. H. Irvine. 
Maximum Acceptable Weight of Lift. Am. 
Ind. Hyg. Assoc. J., v. 28, No. 4, 1967, 
pp. 322-329. 

21. Stevens, S. S. Psychophysics: 
Introduction to Its Perceptual, Neural, 
and Social Prospects. Wiley, 1975. 

22. Tichauer, E. R. A Pilot Study of 
the Biomechanics of Lifting in Simulated 
Industrial Work Situations. J, Safety 
Res., V. 3, No. 3, 1971, pp. 98-115. 

23. Zadeh, L. A. Fuzzy Sets. In- 
formation and Control, v. 8, June 1965, 
pp. 338-353. 



61 




HORIZONTAL DISTANCE OF CENTER OF GRAVITY 
OF LOAD FROM SPINE, in 

FIGURE 1. . Maximum weight versus horizon- 
tal distance from spine based on 1,100 lb and 
1,540 lb of compression on spine, respectively. 



C 



0> 

a. 





8 


>- 




< ) 




2 


^ 


LU 




Z) 


6 


cjr 




LU 




QC 


5 


Ll_ 






4 




3 




2 




Straight back, 
_ bent knee 
(floor to 2. 5 ft) 
I 



30 60 90 

WEIGHT OF THE LOAD, lb 

FIGURE 2. = Effect of lifting technique and fre- 
quency of lift on weight of load that can be lifted 
to maintain metabolic energy expenditure of 5 
kcal/min. 



62 



BOX SIZE, in 
18 19 20 21 22 23 24 25 26 27 28 29 




0.1 0.2 03 0.4 0.5 0.6 0.7 0.8 0.9 I 2 4 

FREQUENCY, lift per minute 

FIGURE 3. - Lifting capacity norms for males (floor-to-knuckle height). 



8 10 12 



a 

UJ 


0.9 


z 




m 


.8 


S 




o 




o 


.7 


U-y) 




Oy) 


6 


>^ 




I-? 




^^ 


.5 


m 




^ 


.4 


Q. 




U 




O 


.3 


O 




< 






.2 








I I I I I I I I I I I I I I I 
R= 1.0 



/ - 



„c 



• •••• * 

^* • • 



■ I ■ I . I . I . I . I 



1.0 



2 0.4 0.6 0.8 I.O 



ACCEPTABILITY OF PSYCHOPHYSICAL 
STRESS 

FIGURE 4, - Acceptability of the combined bio- 
mechanical and physiological stress versus the 
acceptability of the psychophysical stress. 



if) 

< 

UJ 



>• .5 - 



CD 
< 

I- 
Q. 
UJ 
O 
O 
< 





1 


Lifts per minute 
1-12 3-3 
2-9 4-0.1 

1 1 


1 



440 880 1,320 1,760 2,200 

COMPRESSIVE FORCE, lb 

FIGURE 5. - Membership function for biome- 
chanical stress. 



63 



1.0 



UJ 

ir 

ZD 

cn 
< 

UJ 



t .5 - 



CD 

< 
I- 
Q. 
UJ 
O 
O 
< 



\ 

0.7929 \ 


>^ Frequency 
^v =9,12 


- 


Frequency ^s^ 
= 0.1,3 \^ 


1 


0.886 L/min 
1 1 



0.5 I 1.5 2 

OXYGEN CONSUMPTION, L/min 

FIGURE 6. - Membership function for physio- 
logical stress. 




20 30 40 50 60 70 80 90 
WEIGHT OF LOAD, lb 

FIGURE 7, - Membership function of psycho- 
physical stress. 



Operator 
capacity 




Operator 
characteristics 



Task 
characteristics 



Environmental 
characteristics 




Biomechanical 
demands 



Physiological 
demands 



Psychological 
demands 




Comparison 



Percent 
accommodated 



Total 
demand 



Psychophysical 
demand 



FIGURE 8. - A model of lifting performance. 



64 



JOB DESIGN FOR MANUAL MATERIAL HANDLING TASKS 
By M. M. Ayoub,1 J. L. Selan,2 and H. P. R. Rao3 



ABSTRACT 



A procedure for job design of and em- 
ployee placement into manual material 
handling (MMH) tasks based on job demand 
and employee capacity is discussed. The 
first step involves an extensive analysis 
of selected jobs in terms of injury data 
(nature of injury, number of lost work- 
days, etc.) and lifting requirements of 
the job (weight, frequency, range of 
lift, etc.). The measure of job stress 
to be used is a job severity index (JSI). 
The JSI is the ratio of the job demand to 
the capacity of the person or population 



working under the job conditions, ex- 
pressed as the time frequency weighted 
average of the maximum weight required by 
each task divided by the smallest lifting 
capacity given the lifting task condi- 
tions. The JSI provides a means to mea- 
sure job severity and to define the rela- 
tionship between this measure and an ac- 
ceptable measure of injury potential. 
Procedures for job design and employee 
placement based on the JSI are discussed 
and examples are given. 



INTRODUCTION 



A large number of work injuries in 
the industrial arena arise either direct- 
ly or indirectly from the handling and/ 
or mishandling of materials. National 
Safety Council (8^)'* statistics indicate 
that 27 pet of all industrial injuries 
were associated with MMH; this percentage 
equaled 590,000 injuries with a total 
cost of approximately $10.4 billion. 
More important, the number of MMH-related 
injuries continues to increase (670,000 
injuries in 1980 based on National Safety 
Council estimates) despite improved medi- 
cal care, increased automation in indus- 
try, and more extensive use of preemploy- 
ment examinations. 

More imposing than the increase in 
the number of work injuries is the in- 
crease in the cost of these injuries. 
The economic costs associated with MMH- 
related injuries include medical costs, 
lost worktime, insurance-related costs, 
loss of material and property damage, 
lost wages, training cost of a new 
worker, and administration costs. The 

'Horn professor of industrial and bio- 
medical engineering. 

^Research associate. 

■^Research associate. 

Texas Tech University, Department of 
Industrial E^ngineering, Lubbock, TX. 



relationship between these costs and back 
injuries over a 33-yr span (1957-90, pro- 
jected) is exponential as shown in figure 
1 [based on National Safety Council esti- 
mates; from Aghazadeh (J_) ] . The alarming 
rate of increase in the cost of back in- 
juries has also been reported by Snook 
(11). During the 1938-65 period, the 
number of compensable back injuries in- 
creased by 11.4 pet while the average 
cost per back injury increased by approx- 
imately 400 pet. 

The mining industry contains several 
jobs in which MMH activities, in particu- 
lar manual lifting, constitute a major 
component of the job (10) . A listing of 
some of these jobs is given below. 

Jackleg drilling 

Stoper drilling 

Tmbering 

Steel set construction 

Concrete construction 

'^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



65 



Gunite and shotcreting 

Rock dusting 

Loading powder bags 

Ventilation and pipe installation 

Track installation and maintenance 

Given this prevalence of MMH activities 
in the mining industry, it would not be 
surprising to find a large number of in- 
juries including back injuries among min- 
ers. It has been reported (_8) that in 
Pennsylvania 4.8 pet of all con^)ensable 
back injuries were from miners. A study 
presently being conducted for the Bureau 
of Mines (5) also indicates indirectly 
the presence of worker injuries in the 
mining industry. As part of the ongoing 
study (5), isometric strength tests are 
being conducted on miners, provided at 
the time of the test, the miner is not 
suffering from a back injury of any kind. 
Over 10 pet of all miners in the study 
have reported back injuries (although 
it has not been determined in the study 
whether the injuries were directly work 
related). It has been noted in another 
recent study conducted for the Bureau of 
Mines (2), that the heavy lifting demands 
and awkward postures imposed in low- 
coal mining (seam height <48 in) may re- 
sult in an increased probability of back 
injuries. 

Nordby {9) reported that, out of 8 mil- 
lion low-back problems that occurred in 
1974, 200,000 required surgical treat- 
ment. Because of the severity, fre- 
quency, and cost of MMH-related injuries, 
procedures for job design of and employee 
placement into MMH tasks need to be 
seriously considered, properly developed, 
and applied. Such procedures should be 
based on job demands and worker capacity, 
and need to be validated in the work 
environment. The means to determine 
worker capacity has been discussed else- 
where (6), therefore, only a brief sum- 
mary will be presented here. 

The variables affecting lifting capac- 
ity fall into three general categories: 



worker, task, and environmental. Worker 
variables include such factors as body 
weight, sex, age, training, etc. Task 
variables include frequency of lift, 
range of lift, load size, and others. 
Some significant environmental variables 
include heat stress, floor stability, 
traction, etc. There are three different 
bases for determining lifting capacity. 
These are the biomechanical basis, the 
physiological basis, and the psychophysi- 
cal basis. For the biomechanical basis, 
estimates are made of the stresses im- 
posed on the musculoskeletal system while 
lifting. Limits for these stresses are 
established from which the capacity or 
loads to be lifted can then be estimated. 
Similarly, the physiological basis sets 
upper limits based on metabolic or car- 
diovascular criteria (e.g., percent of 
physical work capacity) and then deter- 
mines lifting capacity as some percentage 
of the physiological indice(s). 

As noted by Ayoub (^) , the problem with 
using either the biomechanical or physio- 
logical approach is that both stresses 
are present in any lifting activity. The 
third basis, psychophysical, attempts to 
combine the biomechanical and physiologi- 
cal stresses under a measure of perceived 
stress on the part of the individual. 
The measure of lifting capacity used in 
conjunction with psychophysical methods 
is the "maximum acceptable" or "maximum 
safe weight of lift," defined as the max- 
imum weight an individual feels he or she 
could lift repeatedly without undue 
stress or overtiring. 

The purpose of this paper is to propose 
the use of the JSI developed by Ayoub (_3) 
as a means to define the relationship be- 
tween an acceptable measure of injury po- 
tential and a measure of job severity. 
Also, this paper proposes the use of the 
procedures outlined by Ayoub (3^) , based 
on the work done with the JSI, for job 
design of and employee placement into MMH 
tasks based on job parameters and employ- 
ee capacity. The JSI will be defined in 
the following section, and in the final 
section the job design-employee placement 
procedures based on the JSI will be 
discussed. 



66 



THE JOB SEVERITY INDEX 



DEVELOPMENT 

The JSI conceptually is the ratio of a 
measure of job demand to a measure of the 
capacity of the person or population per- 
forming the job under the job conditions. 
A large JSI represents a relatively 
stressful job. 

The job demands are determined using a 
detailed job description procedure. The 
initial step in the job description pro- 
cedure is to determine the average length 
of the work week, the average length of 
the workday or shift, the number of 
shifts per day, and a general written 
description of the job. This information 
is primarily used to determine the aver- 
age job exposure time of the employees. 

The next step is to describe each job 
in terms of actual weight of lift, fre- 
quency of lift, load size, and range of 
lift. Because many jobs display a lack 
of constant parameters (e.g., several 
frequencies of lift are required), each 
job is divided into a number of component 
tasks such that each task can be de- 
scribed with constant or near constant 
parameters. Thus, each job is described 
as a series of lifting tasks described in 
terms of frequency of lift, range of 
lift, etc. 

Range of lift is defined in terms of 
lift initiation level and lift termina- 
tion level. The load size or dimension 
is defined in terms of inches along a 
line perpendicular to the frontal plane 
of the body of the person doing the lift- 
ing. Lifting frequency is defined as the 
average number of lifts per minute re- 
quired by the particular task. 

The JSI is designed specifically for 
those jobs requiring lifting as a sub- 
stantial portion of the job. As such, 
MMH activities, such as carrying, push- 
ing, or pulling, are excluded from 
analysis. However, the job description 



procedure can be applied to lowering 
tasks (which were found by Ayoub (3) to 
occur in significant amounts in most jobs 
requiring lifting). 

The measure of lifting capacity used by 
the JSI is the maximum acceptable weight 
of lift determined based on psychophysi- 
cal data. As noted, maximum acceptable 
weight of lift is defined as the maximum 
weight an individual feels he or she can 
lift repeatedly without undue stress or 
overtiring. Ayoub (3) developed a set of 
mathematical models to predict the maxi- 
mum acceptable weight of lift based on 
various conditions of lifting frequency, 
load size, and range 
with a few strength 
measurements. These 
are presented in table 
developed for each 
ranges of lift: 



of lift, coupled 
and anthropometric 
regression models 
1. One model was 
of the following 



Floor to knuckle (F-K) 
Floor to shoulder (F-S) 
Floor to full reach (F-R) 
Knuckle to shoulder (K-S) 
Knuckle to full reach (K-R) 
Shoulder to full reach (S-R) 



These models have R2 values 



of between 

0.85 and 0.877. It should be noted that 
these equations predict the sum of the 
maximum acceptable weight of lift plus 
body weight. The sex code is for 
males and 1 for females. The weight 
code is if body weight is below the 
median and 1 if body weight is above the 
median for the male or female population. 
The median body weights for females and 
males are 138 and 170 lb, respectively. 
All strength variables are in pounds, age 
is in years, endurance in minutes, 
and anthropometric variables are in 
centimeters. 



67 



TABLE 1. - Prediction models for maximum acceptable weight of lift plus body weight 
for both males and females 



Lifting 


Constant 


Sex 


Weight 


Arm 


Age 


Shoulder 


Back 


Abdomin- 


Dynamic 


range 


term 


code 


code 


strength 




height 


strength 


al depth 


endurance 


F-K 


-72.165 


-28.334 


24.243 


0.143 


-0.553 


1.225 


0.056 


4.914 


1.757 


F-S 


-145.412 


-16.165 


11.928 


.185 


-.597 


1.438 


.077 


6.472 


2.608 


F-R 


-41.267 


-19.453 


16.176 


.210 


-.892 


.759 


.068 


6.220 


1.426 


K-S 


-55.160 


-18.542 


11.700 


.265 


-.606 


.768 


.105 


6.290 


1.415 


K-R 


-79.193 


-18.917 


17.273 


.297 


-.499 


.092 


.018 


5.154 


2.120 


S-R 


-37.439 


-19.584 


20.352 


.096 


-.592 


.886 


.099 


4.731 


1.090 



F-K 
F-S 



Flo 
Flo 



or to knuckle, 
or to shoulder. 



F-R Floor to full reach. 
K-S Knuckle to shoulder. 



K-R Knuckle to full reach. 
S-R Shoulder to full reach. 



As noted, the JSI is a function of the 
ratio of job demands to worker capacity. 
Specifically, the JSI is the time and 
frequency weighted average of the maximum 
weight required by each task divided by 
the smallest capacity of those associated 
with lifting ranges required by each 
task. The JSI is stated algebraically as 
follows: 



Dayst = total days per week for job. 

Hours I = exposure hours per day for . 
group i, 

Hours^ = number of hours per day that 
a job is performed, 

F: = lifting frequency for task j, 



n 
JSI = E 



Hours j 
Hours-|- 
= 1 



Days j 
Days -I- 



£ix"^ 



j = 1 



CAPj 



where n = number of sub-task groups , 



F, = 



WTj 



total lifting frequency for 
group i, 

maximum weight of lift re- 
quired by task j , 



mj = number of task in group i. 

Days I = exposure days per week for 
group i, 



and CAPj 



the smallest applicable maxi- 
mum acceptable weight of 
lift adjusted for frequency 
of lift and load size. 



FIELD VALIDATION 



Field validation of the JSI was con- 
ducted by Ayoub in 1978 and 1982 {2-^). 
The purpose of both studies was to at- 
tempt to define the relationship between 
MMH injury and the JSI. In general, the 
methodology employed in both studies was 
to evaluate the stress levels of indus- 
trial subjects working in different lift- 
ing jobs and relate the JSI to the injury 
rates experienced by the same group of 
subjects. 

The first step in the field study phase 
was the selection of jobs for analysis. 
Selection was based on the extent that 
the job involved MMH and specifically 



lifting (e.g., a MMH job involving push- 
ing would be excluded). Taking the 1978 
and 1982 studies O-M together, a total 
of 101 jobs involving 385 male and 68 fe- 
male industrial workers from 2 private 
companies and governmental agencies were 
used in the field validation. 

The selected jobs were analyzed in 
terms of lifting requirements of the job 
(procedure and parameters used were dis- 
cussed earlier) and in terms of injury 
data. Information collected describing 
injuries included injury type, injury 
cause (lifting or nonlif ting) , number of 
days lost, medical expenses, wages paid 



68 



during lost workdays, worker's compensa- 
tion paid, and extraordinary expenses. 
Injury type elassif ieations are given 
below. 

Type 1. Musculoskeletal injuries to 
the back. 

Type 2. Musculoskeletal injuries to 
other body parts. 

Type 3. Surface tissue injuries due to 
impact. 

Type 4. Other surface tissue injuries. 

Type 5. Miscellaneous injuries. 



Individual JSI 
each industrial 
JSI values were 
JSI values great 
or less than 0.7 
equal to or les 
1.5 and equal t 
greater than 2.2 
exposure times 
group were then 



's were calculated for 
subject. The resulting 
grouped into four ranges: 
er than 0.00 and equal to 
5, greater than 0.75 and 
s than 1.5, greater than 
o or less than 2.25, and 
5. The injury data and 
for the subjects in each 
compiled and summed. 



Figure 2 shows the relationship between 
JSI and the number of back injuries sus- 
tained per 100 full-time-equivalent (FTE) 
employees (equal to 200,000 exposure 
hours) for the 1978 and 1982 studies O- 
h) combined. Figure 3 shows the rela- 
tionship between JSI and the number of 
disabling (one or more lost days) back 
injuries sustained per 100 FTE employees 
for the combined studies. Figure 4 shows 



the relationship between JSI and the 
severity (number of days lost per disab- 
ling back injury) of disabling back inju- 
ries. Figure 5 shows the relationship 
between JSI and total direct injury ex- 
pense (defined as the sum of medical ex- 
penses, wages paid during lost workdays, 
and worker's compensation) using data 
from the 1982 study (M« For most of the 
parameters, substantial increases oc- 
curred at JSI levels equal to or greater 
than 1.5, and for a number of parameters 
(most notably severity of disabling back 
injuries) there occurred another substan- 
tial increase at JSI levels of 2.25 or 
above. 

Also determined was a stress measure 
for each of the 101 jobs selected for 
analysis. Following determination of the 
stress measure, each job was placed into 
one of the three following categories: 
Jobs that overstressed less than or equal 
to 5 pet of the sample population, jobs 
that overstressed more than 5 pet but 
less than 75 pet of the sample popula- 
tion, and jobs that overstressed more 
than 75 pet of the sample population. 
That proportion of the sample population 
for each job with JSI values greater than 
1.5 was defined as the percentage over- 
stressed for the job. 

Table 2 shows the injury and cost sta- 
tistics calculated for each job stress 
category for the 1978 and 1982 studies 
(3-4), respectively. As percentage over- 
stressed increased, both injury rates and 
costs increased. 



TABLE 2. - Number of back injuries, number of disabling back injuries, days lost per 
disabling back injury, and total expenses observed in various job stress categories 

(Per 100 full-time-equivalent employees (200,000 exposure hours) caused by lifting) 



Population 

overstressed, ' 

pet 


Back 


Disab- 
ling 


Days 
lost 


Total 
expense 


Population 

overstressed, ' 

pet 


Back 


Disab- 
ling 


Days 
lost 


Total 
expense 


1978 DATA, 63 JOBS 


1982 DATA, 38 JOBS 


<5 


5.33 

5.59 

12.04 


5.44 
1.93 
8.76 


2.3 

9.5 

14.1 


NA 
NA 
NA 


<5 


4.18 
16.79 
23.84 



12.60 
17.03 



15.6 
13.4 


NA 


<5, <75 

>75 


75, <75 

>75 


$35,092 
$36,337 



NA Not available. 

'Defined as that proportion of the sample population for each job with JSI values 
greater than 1.5. 



69 



SIGNIFICANCE OF JOB SEVERITY INDEX 



The JSI can be used as a tool for job 
design and employee placement using the 
relationship between JSI injury frequency 
and/or job severity. For job design, the 
following procedure can be followed: 

Step 1. Describe the job as a series 
of tasks, each having a weight distribu- 
tion, average frequency, and ranges of 
lift. 

Step 2. Select an acceptable injury 
frequency based on company policy. 



Step 2. Determine the JSI for the per- 
son if placed at a given job using the 
JSI equation. 

Step 3. Use this JSI to determine the 
expected injury frequency rate if placed 
on that job. Table 3 can again be 
referenced. 

Step 4. Make the screening and place- 
ment decision based upon the acceptabil- 
ity of the injury frequency rate deter- 
mined in step 3. 



Step 3. Select the population for 
which the job is to be designed (for ex- 
ample, 95 pet of the population, females, 
etc.). 

Step 4. Using step 2, determine the 
corresponding JSI from the available 
data. (Such data have been collected by 
Ayoub {3), see table 3.) 

Step 5. For each task (a) select the 
smallest of the predicted lifting capaci- 
ties using the appropriate equation from 
table 1 (e.g. , if a task requires three 
lifting ranges, select the smallest ca- 
pacity of the three) and (b) calculate 
the maximum design weight of lift for a 
task using the JSI equation. 

Step 6. If for a given task, the re- 
quired weight of lift is above the maxi- 
mum designed weight of lift, the job 
should be redesigned in terms of required 
range of lift, frequency of lift, etc. 

To use the JSI for employee placement, 
the following procedure should be 
followed: 

Step 1. Collect the information and 
make the measurements necessary to pre- 
dict the individual's lifting capacity 
for each of the six lifting ranges us- 
ing the predictive models given in ta- 
ble 1. As noted, this information in- 
cludes sex, weight, age, arm strength, 
shoulder height, back strength, abdominal 
depth, and dynamic endurance. 



TABLE 3. - Expected frequency of total 
injuries ' as a function of JSI (_3) , 
warehousing industry 



Frequency 
expected^ 

28. ...r 


JSI 

. 

.0489 
.1244 
.1998 
.2752 
.3506 
.4261 
.5015 
.5769 
.6523 
.7277 


Frequency 
expected^ 

50 

60 

70 

80 

90 


JSI 
0.8032 


30.... 




1.1803 


32. ... 




1.5574 


34.... 




1.9345 


36.... 




2.3116 


38.... 




100 

120 

150 

200 

232 


2.6888 


40. ... 




3.4430 


42.. .. 




4.5754 


44.... 




6.4599 


46.... 




7.6449 


48 






'Sum 

tions. 

2per 


of 1 
100 


the 5 inju 
full-time 


ry type classifica- 
-equivalent employees 



(200,000 exposure hours). 

The JSI has been successfully utilized 
in a number of industrial settings. As 
an example of the practical application 
of the JSI, Liles (_7) performed an analy- 
sis of selected jobs involving MMH for 
Western Electric Corp. The analysis re- 
sults for each job were presented in a 
three-part summary and are presented in 
tables 4 through 6. Table 4 presents the 
job information necessary for the JSI 
calculations. Table 5 gives the JSI's of 
a large representative population of peo- 
ple working in MMH activities. This por- 
tion of the analysis results was conduct- 
ed under the assumption that the large 



70 



TABLE 4. - Job description information for job 99 (7) 



Task 1: 

Maximum weight lb.. 50 

Lifting frequency 1.0000 

Maximum box size... ft.. 5 
Load center of gravity: 

Initial 9 

Terminal 15 

Load height, in: 

Initial 12-22 

Terminal 25-35 

Task: 

Hours 8 

Days 5 



Task 2: 

Maximum weight lb.. 30 

Lifting frequency 1. 0000 

Maximum box size... ft.. 2 
Load center of gravity: 

Initial 8 

Terminal 8 

Load height, in: 

Initial 25-35 

Terminal 30-40 

Task: 

Hours 8 

Days 5 



TABLE 5. - Statistics for representative 
population assumed to be working in 
job 99 (7) 





Population 
percentile 


JSI 




Male 


Female 


Task 1 


95 
50 

5 

95 

50 

5 


3.70 

1.27 

.84 

2.22 
.76 
.50 


50.00 


Task 2 


2.61 
1.29 

30.00 




1.56 
.78 



TABLE 6. - Actual JSI values for persons 
working in job 99 (7) 



Subject 



Female. 
Male. . . 



JSI 

2.1021 
.8787 



size of the assumed population would pro- 
vide a better indicator of the JSI than 
the small group of people actually work- 
ing on the jobs. Finally, table 6 pre- 
sents the JSI values for the people actu- 
ally working at the particular job. 

In comparing the data presented in 
tables 5 and 6, it should be noted that 
the JSI values for the representative 
population of MMH workers (table 5) are 
significantly larger than for the actual 
population working in job 99. This would 
imply that an employee placement proce- 
dure of at least a subliminal level is 
being carried out. Unfortunately for 



industry, this nonf ormalized method of 
employee placement is generally of a hit- 
or-miss nature, and the misses in indus- 
try often surface as injured workers. 
The use of a formalized, empirically 
based employee placement procedure (rath- 
er than, for example, the supervisor de- 
ciding a worker looks strong enough to 
perform the job) such as the JSI could 
potentially reduce the number of injuries 
caused by the wrong worker being placed 
on the wrong job. 

Acceptable and unacceptable weights of 
lift as determined through use of the JSI 
can be compared with lifting guidelines 
predicted using other procedures. Figure 
6 compares the limits for a floor- 
to-knuckle lift at various lifting fre- 
quencies obtained using the JSI and using 
the protocol recommended in the NIOSH 
guide ( 12 ) for manual lifting. The maxi- 
mum permissible limit (MPL) and action 
limit (AL) lines generated using the 
NIOSH equations correspond roughly with 
the 2.25 and 1.125 JSI lines, respective- 
ly, in that lifting tasks above 2.25 or 
the MPL fall in the unacceptable range 
(i.e., require engineering controls), 
tasks below 1.125 or the AL represent a 
nominal safety risk, and tasks falling 
between the criterion limits (1.125-2.25, 
AL-MPL) require administrative control. 
It is apparent that the AL and, to a 
lesser extent, the MPL are more conserva- 
tive than the corresponding JSI lines; 
this being particularly true for higher 
frequencies of lift. 



SUMMARY 



71 



It can be said that the ratio of job 
demand to the capacity of the worker does 
affect the frequency and severity of in- 
juries incurred during MMH activities. 
Use of the JSI provides a means to con- 
trol these injuries through redesign of 
demand tasks and/or (as a last resort) 



better placement of workers. Because of 
the presence of MMH activities in the 
mining industry, the JSI has the poten- 
tial to reduce the frequency and severity 
of MMH-related injuries in this indus- 
trial area. 



REFERENCES 



1. Aghazadeh, F. Simulated Dynamic 
Lifting Strength Models for Manual Lift- 
ing. Unpublished Ph.D. Dissertation, 
Texas Tech. University, Lubbock, TX, 
1982; available upon request from M. M. 
Ayoub, Texas Tech Univ., Lubbock, TX. 

2. Ayoub, M. M. , N. J. Bethea, 
M. Bobo, C. L. Burford, K. Caddel, K. 
Intaranont, S. Morrissey, and J. Selan. 
Biomechanics in Low Coal Mines contract 
H0387022; for inf., contact S. J. Mor- 
risey, Pittsburgh Res. Center, Pitts- 
burgh, PA. 

3. Ayoub, M. M. , N. J. Bethea, S. 
Deivanayagam, S. S. Asfour, G. M. Bakken, 
D. Liles, A. Mital, and M. Sherif. De- 
termination and Modeling of Lifting Ca- 
pacity. Final Rept. NIOSH, grant 5R010H- 
00545-02, September 1978; available upon 
request from M. M. Ayoub, Texas Tech. 
Univ. , Lubbock, TX. 

4. Ayoub, M. M. , D. Liles, S. S. As- 
four, G. M. Bakken, A. Mital, and J. 
Selan. Effects of Task Variables on 
Lifting Capacity. Final Rept. NIOSH 
grant 5R010H00798-04, August 1982; same 
as ref. 3. 

5. Ayoub, M. M. , J. L. Selan, C. L. 
Burford, H. P. R. Rao, K. Intaranont, M. 
Bobo, K. Caddel, and J. L. Smith. Bio- 
mechanical and Work Physiology Study in 
Underground Mining Excluding Low Coal. 
Ongoing BuMines contract J0308058; for 



inf., contact J. M. Peay, Pittsburgh Res. 
Center, Pittsburgh, PA. 

6. Ayoub, M. M. , J. L. Selan, W. Kar- 
wowski, and H. P. R. Rao. Lifting Capac- 
ity Determination. See preceding paper 
in this proceedings. 

7. Liles, D. Analysis of Selected 
Materials Handling Activities for Western 
Electric. Report to company, 1981; 
available from M. M. Ayoub, Texas Tech. 
Univ., Lubbock, TX. 

8. National Safety Council. Accident 
Facts. Chicago, IL, 1978. 

9. Nordby, E. J. Epidemiology and 
Diagnosis in Low Back Injury. J. Occupa- 
tional Health and Safety, v. 50, No. 1, 
1981. 

10. Selan, J. L. , M. M. Ayoub, and 
H. P. R. Rao. Manual Materials Handling 
in the Mining Industry. Unpublished re- 
port; available upon request from M. M. 
Ayoub, Texas Tech. Univ., Lubbock, TX. 

11. Snook, S. H., and V. M. Ciriello. 
Low Back Pain Industry. Am. Soc. Safety 
Eng. J., V. 17, No. 4, 1972, pp. 17-23. 

12. U.S. Department of Health and Hu- 
man Services. Work Practices Guide for 
Manual Lifting. NIOSH, Pub. 81-122, 
1981, 183 pp.; NTIS PB 82-178-948. 



72 




I960 1970 1980 1990 

YEAR 

FIGURE 1. - Cost of trunk injuries over time (1). 



(T 

O 

X 

LU 

cr 

CO 
O 

a. 

X 

UJ 

o 
o 

o" 

o 

CvJ 

cr 

UJ 

a. 



20 



10 



ra 

i 



.*-■' 



A- 



i 



a"^ 



.>^^ 



i 



.'V^ 






.^^ 



T? 



JSI RANGE 

FIGURE 2. - The incidence of back injuries 
caused by lifting versus JSI. 



73 



ir 
I 20 



•^ LlI 

o tr 
< 3 
m t/> 
o 
o a 

_1 1^ 

<8 

'-' C\i 
QL 

uj q: 

QQ UJ 
=> CO 



a: 

3 



I 5 



10 



5 - 



1 1 


n 
/ 






- 



.^ 



.^ 



^^ 



'p 






0.- 



\- 



JSI RANGE 



FIGURb 3. - The incidence of disabling back 
injuries caused by lifting versus JSI, 




JSI RANGE 



FIGURE 4. - The severity of disabling back 
injuries caused by lifting versus JSL 




JSI RANGE 

FIGURE 5. - The total expense of back injur- 
ies caused by lifting versus JSI. 



125 I 1 1 1 1 1 1 1 I r 



Maximum 
permissible 
" limit 




I 



2345 6789 

LIFTS PER MINUTE 



FIGURE 6. - Comparison of lifting guides based 
on JSI versus NIOSH (12) lifting guidelines. 



74 



BACK INJURIES AND MAINTENANCE MATERIAL HANDLING IN LOW-SEAM COAL MINES 
By Ernest J. Conway' and William W. Elliott2 

INTRODUCTION 



Accidents associated with the handling 
of materials and supplies have tradition- 
ally accounted for a large percentage of 
all industrial lost-time injuries. The 
National Safety Council reports that this 
accident category is responsible for at 
least 25 pet of all industrial accidents. 
In the mining industry, an even higher 
percentage of materials handling injuries 
are noted. As table 1 suggests, these 
statistics are relatively consistent 
across various types of mining opera- 
tions. Somewhat higher percentages, how- 
ever, are noted for underground coal 
mines and for metal processing plants. 

TABLE 1. - Materials handling injuries 
by industry by work location, January- 
March 1982' 



Coal mines: 

Underground 

Surface 

Preparation plant.. 
Metal mines: 

Underground 

Surface 

Mills 

Total or percent. 

'Mine Injuries an 
ly , January-March, 
ment of Labor, Mine 
Administration. 



Handling 


Lost time 


injuries 


injuries 


Total 


pet 


1,115 


3,211 


34.7 


175 


628 


28.0 


68 


233 


29.0 


93 


337 


27.5 


51 


150 


34.0 


71 


193 


36.7 


1,573 


4,752 


33.1 



d Worktime Quarter- 

1982, U.S. Depart- 

Safety and Health 



^Vice president. Canyon Research Corp., 
Westlake Village, CA. 

^Fire systems engineer, Santa Barbara 
Research Center, Subsidiary of Hughes 
Aircraft Co., Santa Barbara, CA. 



Table 2 summarizes manual materials 
handling injuries in 26 mines at several 
points in the mine supply cycle. It is 
noted that the largest single source of 
injury involves the movement of supplies 
and components from the surface to the 
point of use in the mine. This function, 
however, may involve handling of the same 
material two, three, or more times prior 
to reaching the point of use. The second 
largest category, which accounts for 
approximately 26 pet of all injuries, 
occurs during the actual use of the mate- 
rials in mine maintenance or equipment 
repair activities. These are the acci- 
dents to be discussed in this paper. For 
purposes of the following discussion, 
materials handling shall be defined as 
the lifting, pushing, pulling, or shovel- 
ing of materials or components used dur- 
ing equipment maintenance or during mine 
maintenance activities. 

TABLE 2. - Analysis of in-mine material 
handling injuries for 26 mines 

Injuries , 
Handling mode pet 

On-section manual handling of 
equipment and or supplies 
during production shift 11.2 

Supply movement from surface 
to point of use 49.5 

Section move: Movement be- 
tween working sections 13.0 

Equipment maintenance: During 
maintenance shift 16.3 

Mine maintenance and handling 

on maintenance shift 10.0 

Total 100.0 



75 



ACCIDENT REPORT ANALYSIS 



In an effort to define the magnitude of 
the materials handling injury problem in 
underground coal mines, an analysis was 
performed of over 75,000 accident reports 
collected and reported in the Mine Safety 
and Health Administration Health and 
Safety Analysis Center (HSAC) data base 
for a 3-yr period. 3 This review resulted 
in the identification of 15,416 cases 
that reportedly involved materials han- 
dling activities. These materials han- 
dling accident reports were then sorted 
into the following four categories: 

1. Part of body injured 

2. Type of accident. 

3. Source of injury 

4. Nature of injury 

Table 3 summarizes the 15,416 injury 
reports by part of body affected. It is 
observed that over 39 pet of these re- 
ported injuries involved the middle and 
lower back. This category represents a 
larger percentage of materials of han- 
dling injuries than the next six elements 
combined. 

Table 3 also summarizes the same 15,416 
cases by type of accident. It is noted 
that the largest single accident category 
is overexertion while lifting. This fre- 
quently involves the lifting of a com- 
ponent (e.g., a shuttle car drive motor) 
or mine supplies (e.g., rock dust bags, 
etc. ) from the ground prior to use. 
Likewise, it is noted that overexertion 
pulling accounts for another 20.6 pet of 
the total injuries. Combined, overexer- 
tion type accidents account for more than 
half of all the injuries. 



■^Ongoing BuMines contract HO1 13018; for 
info. , contact R. L. Unger, Pittsburgh 
Res. Center, Pittsburgh, PA. 



TABLE 3. - Ranking of underground mine 
maintenance material handling injuries 



Rank 



Element 



PART OF BODY 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

NAp 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

NAp 

NAp Not 
NEC Not 



Back 

Finger 

Hand 

Foot 

Hips 

Knee 

Shoulders 

Eyes 

Multiple parts. 

Wrist , 

Neck , 

Chest , 

Leg, NEC , 

Arm, NEC , 

Abdomen , 

Head, NEC , 

Toes , 

Ankle , 

Other , 



ACCIDENT TYPE 



Overexert, lift.... 

Falling object 

Overexert, NEC 

Caught , NEC 

Overexert, pull.... 

Struck by, NEC 

Stationary object.. 
Caught , moving and 
stationary. 

Flying object 

Rolling object 

Overexert, wield... 
Other 



applicable, 
elsewhere classified. 



pet 



39.7 
18.3 
4.9 
4.8 
4.0 
3.6 
3.1 
2.8 
1.8 
1.5 
1.5 
1,4 
1.4 
1.3 
1.3 
1.0 
1.0 
1.0 
<1.0 



31.0 
14.3 
13.1 
8.8 
7.5 
6.7 
6.5 
3.3 

2.6 

1.2 

1.2 

<1.0 



When the materials handling accidents 
are sorted on the basis of the source of 
injury, an interesting distribution is 
observed (table 4). As table 4 suggests, 
a broad spectrum of components and mate- 
rials are involved in the maintenance- 
related handling injuries. As will be 
discussed later, many of these elements 



76 



would probably not have resulted in in- 
juries if they were handled on the sur- 
face instead of in the mine. This type 
of distribution suggests that what is 
handled may not be as important as where 
and how it is handled. 

TABLE 4. - Underground maintenance 
handling injuries summarized by 
source of injury 



Rank 



9.. 

10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 



Element 



Metal, NEC 

Timber posts, cap 

Broken rock, ore... 

Electrical conduit 

Steel rail 

Belt conveyor 

Metal components........ 

Cement products 

Wood items, NEC 

Jacks 

Rock bolts 

Bags 

Barrels , drum 

Chains , ropes 

Underground mine machine 

Miscellaneous, NEC 

Containers , NEC 

Cribbing 

Container, NEC 

Blocking 

Pumps, fans, NEC 



pet 



13.8 
12.8 
8.9 
7.2 
4.6 
3.6 
3.5 
2.9 
2.5 
2.5 
2.4 
2.3 
2.1 
1.9 
1.9 
1.8 
1.6 
1.6 
1.6 
1.4 
1.3 



NEC Not elsewhere classified. 

Perhaps the most revealing summary is 
presented in table 5. This table summa- 
rizes the underground materials handling 
injuries on the basis of the number of 
days lost. Not only do back injuries ac- 
count for the largest percentage of the 
injuries, but they account for an even 
larger percentage of days lost from work. 
This suggests that back injuries are 
somewhat more serious than other types of 
injuries. 

In an effort to identify the specific 
task being performed by the miner at 
the time of the maintenance handling in- 
jury, a second series of analyses were 
performed for the narrative description 
of 5,376 HSAC cases. These cases in- 
volved only in-mine equipment or mine 
maintenance tasks. These accidents were 
sorted into the following categories: 



1. Lifting or lowering 

2. Carrying 

3. Maneuvering 

4. Other activity 

TABLE 5. - Summary of 1978-80 underground 
coal mine material handling accidents, 
HSAC data 



Part of 


Injuries 


Injuries involving 


body 


Total 


pet 


days lost 


injured 


Total 


pet 


Head 

Neck 

Shoulders 

Arms 

Wrists. . . 
Hands .... 
Fingers. . 
Trunk. . . . 

Back 

Hips 

Legs 

Feet and 

toes. . . . 
Other. ... 


889 
230 
474 
451 
226 
752 

2,813 
589 

6,119 
617 

1,079 

880 
291 


5.8 
1.5 
3.1 
2.9 
1.5 
4.9 

18.3 
3.8 

39.7 
4.0 
7.0 

5.7 
1.8 


487 
201 
400 
335 
165 
512 

1,673 
494 

5,606 
400 
920 

736 
253 


4.0 
1.6 
3.3 
2.7 
1.4 
4.2 

13.7 
4.1 

46.0 
3.3 
7.6 

6.0 
2.1 


Total.. 


15,410 


100.0 


12,182 


100.0 



Table 6 identifies the miner's activity 
and the items being handled at the time 
of the accident for equipment maintenance 
tasks. It is pointed out that lifting 
and lowering of components accounted for 
the majority of all the days lost. It is 
also noted that oil drums and grease 
cans , machine parts and tools are the 
most frequently involved items. 

Table 6 also summarizes the miner's ac- 
tivity at the time of the accident by the 
material handled during mine maintenance 
activities. It is observed that lifting- 
lowering of track rails and timbers are 
involved with the largest number of days 
lost from work. This can be anticipated 
since rails and timbers have relatively 
high unit weights and are awkward to han- 
dle. Unfortunately, track laying and 
timber handling is traditionally accom- 
plished manually using only a few simple 
handtools. 



77 



TABLE 6. - 1978-80 underground coal mine material accidents, summarized 
by activity and item being handled 



Activity 



Item 



DURING EQUIPMENT MAINTENANCE ACCIDENTS 



Lifting-lowering. 

Do 

Other activity... 
Lifting-lowering, 

Do 

Do 

Do 

Maneuvering. . . . . , 

Carrying 

Dropping 

Carrying 

Other activity.., 

Do , 

Maneuvering , 

Other activity.., 

Carrying , 

Other activity... 



Oil drum, grease can, hydraulic oil. 

Machine part, tool 

do , 

Pump, motor, gearbox, wheel unit..., 

Cover plate, X-P cover , 

Tire 



Toolbox 

Machine part, tool 

Oil drum, grease can, hydraulic oil. 

Machine part , tool 

Pump, motor, gearbox, wheel unit..., 
Tire 



Oil drum, grease can, hydraulic oil. 
Pump, motor, gearbox, wheel unit.... 

Cover plate, X-P cover 

Machine part , tool 

Pump, motor, gearbox, wheel unit.... 



DURING MINE MAINTENANCE ACCIDENTS 



Lifting-lowering. 

Do 

Do 

Other activity... 

Maneuvering 

Lifting-lowering. 
Other activity... 

Do 

Lifting-lowering. 

Dropping 

Carrying 

Do 

Other activity... 
Dropping 

Do 

Lifting-lowering. 



Track, rail 

Timber, cribbing, ties. 

Crossbar, header 

Timber, cribbing, ties. 

Track rail 

Other 

Track rail 

Crossbar, header 

Stopping block , 

Track rail , 

Other , 

Timber, cribbing, ties. 

Stopping block , 

Timber, cribbing, ties. 

Stopping block , 

Rock dust, cement bag. , 



Days 
lost 



3,629 

2,249 

2,182 

1,749 

1,639 

1,127 

1,070 

692 

559 

537 

490 

434 

349 

334 

314 

301 

289 



1,828 
1,355 
783 
643 
487 
425 
388 
372 
327 
319 
236 
224 
211 
150 
149 
148 



The above analysis has pointed out that 



2. About 40 pet of these injuries in- 
volve the middle or lower back. 



3. Over 30 pet of the injuries result- 
ed from overexertion while lifting or 
lowering objects. 



1. A majority of the in-mine injuries 
involve materials handling activities and 
account for about 34 pet of all lost-time 
injuries. 

CONTRIBUTING FACTOR IDENTIFICATION 

in procedures can minimize the associated 
risk to mine personnel. This is particu- 
larly important for lower seam height 
mines which tend to have more severe 



Through examination of these accident 
data, it is possible to identify factors 
contributing to these injuries. By look- 
ing at some of the biomechanical limita- 
tions of the human body, it is possible 
to identify areas where mechanization of 
materials handling tasks and/or changes 



material handling related back injuries. 4 
^Work cited in footnote 3. 



78 



Why are there relatively higher numbers 
and more severe back injuries in lower 
seam mines? There are several factors 
involved. The most important one, how- 
ever, is the fact that the spine is de- 
signed to carry a maximum load when the 
miner is standing in an erect, upright 
position. In fact, the cervical, thora- 
cic, and lumbar curves in the spine are 
designed to center the load being lift- 
ed (including the body weight of the 
individual) between the ball and the 
heel of the foot. In the fully erect po- 
sition, the human spine typically can 
safely handle up to 100 pet of the per- 
sons 's body weight for short periods of 
t ime . 5 

When the spine is in other than the 
full erect position, however, the load 
that it can safely handle decreases 
sharply. This is the result of — 

1. The load not being evenly distrib- 
uted across the vertebra and the inter- 
vertebral disk. 

2. The muscles being strained simply 
supporting the weight of the upper torso, 
arms, and head. 

3. The ligaments and tendons being 
strained supporting the upper body weight 
and guiding the body's motion. 

More specifically, when the miner is 
bending forward (as in a 48- to 60-in 
seam height), the muscles of the back and 
stomach, which are normally used to main- 
tain balance, must now support the weight 
of the head, upper torso, and arms from a 
biomechanically disadvantaged position. 
This amounts to a substantial amount of 
weight if you consider that 



2. The average arm up to the shoulder 
weighs 12 to 15 lbs. 

3. The upper torso minus the head, 
neck, and arms weighs 70 to 90 lb. 

The back and stomach muscles of the 
typical 190-lb miner are supporting some- 
what over 100 lb of "dead" upper body 
weight when he or she leans forward ap- 
proximately 45°. This moment of force 
must be borne by the lower spine and typ- 
ically acts on the lumbrosacral joint. 
This simply means that the body itself 
(spine, muscles, and ligaments) is in- 
capable of handling as much nonbody 
weight as when the person is standing in 
a full upright position. In an improper 
work position, a load weighing only 30 lb 
combined with the weight of the upper 
body components may produce a torque on 
the lower spine exceeding 300 in* lb. The 
latter is the lifting equivalent of quite 
a severe lifting task. Hence, depending 
upon the miner's build and physical con- 
dition, from 50 to 90 pet of the back's 
muscle strength may be used just to sup- 
port the upper body weight. This sug- 
gests that a person can only safely lift 
considerably less than 50 pet of the 
weight that could be lifted in a normal 
erect position. This percentage is re- 
duced even further if 

1. The miner is sitting on his or her 
knees or buttocks, thus eliminating the 
shock-abosorbing effects of the knees and 
ankles. 

2. The lifting task requires movement 
of the object from one side of the body 
to the other with the feet or knees 
(e.g., in a kneeling position) in a fixed 
position. 



1. The average head (without the neck) 
weighs 20 to 30 lb. 



3. The lifting task requires the 
transporting of the center of mass away 
from the body. 



-'U.S. Department of Health and Human 
Services. Work Practices Guide for Man- 
ual Lifting. NIOSH Pub. 81-122, 1981, 
183 pp.; PB 82-178-948. 



4. The size of the object moves the 
center of mass of the person-object away 
from the body's own natural center of 
gravity. 



79 



Research has shown that a majority of 
the low-back injuries actually occur upon 
release of a heavy load rather than at 
the moment it is picked up. The reason 
for this is that when a load is lifted 
the stress induced to the human body is 
distributed over time (e.g., 0.75 to 1.50 
sec). When the same load is released, 
separation may take place in as little as 
40 sec or one-twentieth of the time re- 
quired to place the load on the spine. 
This results from 

1. Extreme stress induced by muscle 
action required to reestablish the body's 
center of balance. 



2. Sharply increased musculoskeletal 
loading on the vertebra while attempting 
to regain balance. 

To make matters worse, the closer the 
miner's body is to the floor (i.e., 
stooped forward 90°), the greater the 
musculoskeletal stress. 

As table 7 illustrates, many of the 
materials handling tasks performed during 
mine or equipment maintenance involve the 
lifting or handling of items that exceed 
safe lifting weights for persons not in a 
full upright position. 



TABLE 7. - Weight of frequently handled components 



I Unit weight, lb | Frequency | 



Description 



Tools 



EQUIPMENT MAINTENANCE 



Major component replacement. 

Component replacement 

Minor component replacement. 
Lubrication and servicing. . , 

Move workers' tool , 

Repair by welding 



Change tire 

Repair electrical cable 

Access permissible enclosure. 



200-2,000 



50- 

5- 

5- 

50- 

50- 



200 

50 

50 

200 

200 



50- 200 

1- 5 

50- 200 



Monthly 
Weekly. 
Daily.. 
. . .do. . 
Monthly 
Daily.. 

Weekly. 
Daily. . 
. . .do. . 



Jacks , come-alongs . 
Handtools. 

Do. 
Pails, 5-gal cans. 
Toolbox. 
Cutting and welding 

equipment. 
Jack. 
Handtools. 

Do. 



MINE MAINTENANCE 



Set props and crossbars. • 


200- 


500 


to 20 
per day. 


Saw , axe . 






Bui. Id s topping walls ••••••••••••••• 


50- 


100 


2 per day. 
Monthly. . . 


Axe. 


Build ventilation doors 


5- 


50 


Handtools 


Build cribs •••• • 


50- 
100-1 


100 
,000 


Daily 

Monthly. . . 


Axe. 


Install track ••••••••••••• 


Handtools, sledge- 




hammer, pry bars. 


Build overcasts •••••••••••••••••••• 


200- 


500 


Semiannual 


Handtools, axe. 




sledgehammer, pry 










bars. 


Tn t? t" fl 1 1 wp tPT* ninp^ DiiTnns .••>>•>>> 


50- 


100 


Weekly. . . . 
Semiannual 


Handtools. 


Install electrical power boxes 


200- 


500 


Come-alongs , hand- 










tools, scoop. 


RopIc Hitcit hflpic pntries- .....>•••••• 


50- 
5- 


100 
50 


Daily 

. . .do 


None. 


Clean up rib trash, rock falls. 


Shovel, scoop. 


etc. 










Build plank roadways through wet 


50- 


100 


Semiannual 


Scoop. 


areas. 











80 



SUMMARY 



What are the implications of these 
findings for materials handling in lower 
seam mines? First, with this understand- 
ing of the material handling tasks that 
must be performed and the limitations of 
the human spine, innovative approaches to 
the materials handling problem can be 
sought. As reported in another paper in 
this proceedings , the Bureau of Mines is 
currently developing a number of innova- 
tive handling devices. 

Secondly, improved materials handling 
procedures and practices need to be de- 
veloped. The straight-back lifting tech- 
nique is simply not effective in mines 
where the miner cannot stand upright. 
Research is needed to find an alterna- 
tive approach. Likewise, procedures that 



better utilize the tools and equipment 
found in the mine environment to do the 
materials handling need to be identified, 
thereby eliminating stress on the miner's 
back. 

Third, equipment used in mines needs to 
be designed so that it can be properly 
and safely maintained in the restrictive 
mine environment. The size and weight of 
supplies and materials used in mine main- 
tenance needs to be reduced to ensure 
that they can be "safely" handled by the 
miner. 

Finally, every miner must understand 
the limitations of the human back and he 
or she must take the precautions neces- 
sary to prevent injury. 



81 



TRAINING PROCEDURES TO REDUCE LOW BACK INJURIES 
By Nancy C. Selby ' 



ABSTRACT 



Many back, injuries can be avoided, as 
can chronic back pain. However, individ- 
uals need to have enough information to 
be able to understand how to protect 
themselves. Safety information must be 
presented in a manner that is relative to 
individuals' environment and educational 
level. Since most back injuries do not 
occur on the job, first aid and home 



activities must be included in training 
programs. Lifting instructions are only 
a small part of total effective injury 
prevention; proper sitting, standing, 
pushing, pulling, and turning procedures 
must also be included. The blue collar 
worker can and will take responsibility 
for his or her own back care with proper 
training. 



INTRODUCTION 



Second only to the common cold, back 
injuries and back pain are the most fre- 
quent problem in the work force in the 
United States. Over 75 pet of the popu- 
lation suffers from back pain at some 
point in time. Back pain interferes with 
worklife and social habits. In 1980, it 
accounted for 93 million lost-time days, 
as well as $5 billion in medical costs 
and $12 billion in legal and insurance 
fees (11).2 These figures have risen in 



the past 2 yrs. Back injuries may ac- 
count for only 25 pet of all injuries, 
but cost over 65 pet of the dollars 
spent. Back pain and back injuries have 
become one of the most expensive health 
problems in the mining industry just like 
every other industry in the United 
States. Unfortunately, knowing that 
"everybody has it" does not alleviate the 
discomfort or the frustration that accom- 
panies back pain. 



DISCUSSION 



Back injuries are frustrating because 
they are so difficult to identify, diag- 
nose, and treat. Differentiation between 
a "real" injury and a "supposed" injury 
is challenging to the medical community 
as well as to industry. It is not the 
kind of injury that can be casted and be 
healed in a certain length of time (_8 ) . 
Back injuries become a problem of balance 
sheets and productivity versus worker's 
compensation premiums and lost-time days. 

In the underground coal mining indus- 
try, an average of 2,500 back injuries 
per year occurred between 1977 and 1981. 
If the average cost of a back injury is 
$5,000, a yearly expenditure could be 

^Director, Spine Education Center, Dal- 
las, TX. 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



over $12 million. Of course, not all 
back injuries cost $5,000, but some cost 
much more (12). This figure does not in- 
clude those individuals who undergo sur- 
gery or have long-term problems. 

Since back injuries are a fact of life, 
a safety director or personnel manager 
with safety-related duties becomes an in- 
tegral part of the team that tries to 
oversee the problems. Unfortunately, 
that individual is usually consumed with 
paperwork and has neither the time nor 
budget to initiate an effective program. 
So he or she turns the entire dilemma 
over to the supervisors. Supervisors may 
be very knowledgeable about mines and 
mining, techniques and equipment, but 
they rarely have experience in safety and 
injury prevention. Yet, they are the 
people who are made ultimately responsi- 
ble for every back injury on the job. 
There is no way they can stop the back 



82 



pain problem unless they have adequate 
training and management's support ( 15 ) . 

It is not unusual for a typical safety 
program to allocate 0.04 pet of an entire 
budget to safety, which translates to 
$50,000 if the company has a yearly oper- 
ating budget of $130 million (_3 ) . It is 
definitely time to modify the present 
system. Back injuries alone represent a 
costly liability. Training techniques 
must also be modified to stimulate the 
individuals who are doing the work. We 
must remember that all of us are much 
more highly educated and exposed through 
the television media than we once were. 
The American worker expects and should 
receive training that is relevant to his 
or her situation. 

The concept of educating individuals to 
be responsible for their own health care 
has surfaced in recent years. Extensive 
studies have determined that education 
has been the key factor in helping hemo- 
philiacs and diabetics control their 
diseases successfully (13). People with 
back pain have not had much information 
available to them, so they have been un- 
able to control their problems. Back ed- 
ucation and "back school" began in Sweden 
in 1970. In a triple blind study, there 
was substantial evidence indicating that 
education returned patients to work soon- 
er than regular physical therapy modali- 
ties (_1_) . Also, recurring absence from 
work was reduced. 

The group incurring back injuries are 
those individuals who are doing the ac- 
tual labor, not the supervisors. There- 
fore, it is important that the workers be 
trained using appropriate techniques and 
materials. Supervisor participation and 
management support is essential for ef- 
fective results. If given applicable in- 
formation, miners will be able to take 
responsibility for their own back care. 

The program content found to be most 
effective is a comprehensive one that 
consists of information that incorporates 
several topics as they relate to the 
person working in a mine and their poten- 
tial back problems. 



People cannot be expected to take care 
of their back unless they have some un- 
derstanding of anatomy {8). We have a 
spine for two reasons; one is for sup- 
port. The other function of the spine is 
to protect the spinal cord. 

We have a number of anatomical parts 
that affect the way we feel, but the most 
common long-term injury involves the 
disks. Disks rest between the 24 verte- 
brae in our backs. Disks are the shock 
absorbers of our bodies, just like we 
have shock absorbers in our cars. An ef- 
fective training program will use analo- 
gies that are easily understood. For ex- 
ample, disks look a lot like a jelly 
doughnut; crusty on the outside with jel- 
ly on the inside. And everyone under- 
stands what happens if a jelly doughnut 
is crushed; it leaks, just like a disk 
does when it is crushed. Unfortunately, 
when a disk herniates, that jelly may in- 
terfere with the nerves and cause pain 
and neurological deficits that will lead 
to surgery. A ruptured or herniated 
disk is the most common reason for back 
surgery. 

If we are interested in avoiding disk 
herniation, it is necessary to understand 
disk pressure. Different body positions 
put more or less pressure on the low back 
area; extensive studies from Sweden have 
demonstrated this. For example, a person 
who stands with knees locked, bent for- 
ward, will put 200 lb of pressure on the 
low back area (fig. 1). An individual 
who sits incorrectly will do the same 
thing. However, if we can reeducate that 
person to sit with arms and back support- 
ed and knees higher than hips, we can cut 
that disk pressure in half. When lift- 
ing, a person who holds material a fore- 
arm's length away from his or her body 
will put 10 times more pressure on the 
low back than if that same object is held 
close. Fortunately we can put ourselves 
in positions that are comfortable as well 
as beneficial. Lying on your back with 
your feet on a stool puts only 25 lb of 
pressure on the low back (fig. 2). For 
this reason, it is called the resting 
position (7). 



83 



Pressure on the back is directly re- 
lated to body mechanics (6). Body me- 
chanics is not just lifting. It is sit- 
ting, standing, bending, stooping, reach- 
ing, and turning, as well as lifting. In 
employee training, a giant inadequacy has 
been the neglect to educate the worker 
about job-related situations other than 
lifting. 

For example, there are two tribes in 
the world that have no incidence of back 
pain: One is in Mexico, and one is in 
Africa. Apparently, they do not have 
back pain because they do not spend much 
time sitting. Everyone in this country 
spends a great deal of time sitting, 
whether at their job or at home watching 
television, and that is contributing to 
the back pain problem (11). 

We know that absorption of informa- 
tion is directly related to understand- 
ing the subject matter presented ( 10 , 
14). Obviously then, a back injury pre- 
vention program for miners should uti- 
lize visuals of miners in their job 
situation. 

Sitting with knees higher than hips 
takes pressure off the back in situations 
that require sitting. Getting close to 
the worksite and working straight ahead 
takes pressure off the low back area. 
Getting down to the level of the work is 
as important as staying close when reach- 
ing. However, miners have a difficult 
problem because they are forced to stay 
in that position for long periods of time 
(12) . Protecting their backs may con- 
tribute to knee problems. 

Standing with knees locked may not 
cause a back injury, but it can give 
you a very tired back by the end of the 
day. It is recommended that a person 
who stands all day put one foot slightly 
in front of the other with knees slight- 
ly bent. This gives the individual a 
wider base of support so that the back 
is not as likely to be stressed. If a 
piece of equipment is available, putting 
one foot up will take even more pres- 
sure off the back. Bars have railings 
for back comfort while standing and 
drinking. 



Ergonomics plays an important role in 
back injury prevention (6^) . Look for 
simple modifications to install to make 
employees more comfortable. 

Other body mechanics techniques that 
should be discussed are pushing, pull- 
ing, lifting, and pivoting. Pushing is 
usually more desirable than pulling. An 
accident that occurs with frequency is 
pulling with feet parallel — an individual 
using only his or her back — and a mechan- 
ical device close by. 

Lifting, like other jobs, can be done 
in several ways. The person handling ma- 
terial should be as close as possible to 
the object. This is the most important 
concept. Lifting can be accomplished by 
putting one knee down or squatting. It 
is important that the legs be used for 
leverage, not the back (fig. 3). Not 
everyone can lift the same way. People 
and material come in different sizes and 
should be handled accordingly. These 
different options should be demonstrated, 
discussed, and practiced at the time of 
training. Learning to pivot rather than 
twist is particularly helpful. 

Employees need to know how to modify 
their body mechanics and why. It is 
important that employees understand the 
benefits of using good body mechanics 
and the disadvantages if they do not. 
With this knowledge, they can think 
about a job, their back, and the best 
way to avoid pressure when performing 
that job (8). Utilizing mechanical de- 
vices whenever possible will also dimin- 
ish injuries. 

Injuries occur at home, too, and be- 
cause of our system, they may become a 
Monday morning worker's compensation ac- 
cident. Therefore, it is important for 
the miners to be able to transfer these 
new techniques to a home situation. Even 
shaving and brushing teeth can cause back 
pain. An alternative is to bend the 
knees into the sink or put a foot up in 
the cabinet. Doing yard work incorrect- 
ly can cause back pain; driving long 
distances in the car can, too. Most 
Americans drive with the seat too far 
away with knees dropped below hip level. 



84 



Moving the seat forward a notch may alle- 
viate the problem. An inexpensive back 
support can be created by rolling up a 
towel. There are also two-person jobs at 
home, and it is important that safe tech- 
niques be practiced off the job. 

Considering that the majority of the 
population has back pain some time in 
their life, it is sensible to give every- 
one a workable first aid treatment for 
back pain. Most people suffer from back 
pain that involves muscle spasm. The 
most effective treatment found is ice 
massage, stretching, and the use of as- 
pirin. Muscles that are tight and tense 
are in spasm. Ice massage will numb the 
area and allow the knees to be brought up 
toward the chest to stretch those muscles 
out to their normal limits (4, 9). Mus- 
cles only have the capability to contract 
by themselves. If you have ever experi- 
enced a cramp in the foot in the middle 
of the night, you know you have to walk 
on it or rub it. Muscles in the back are 
like that. They have to be stretched to 
their normal limits. The use of ice will 
allow that to occur. Aspirin is a superb 
anti-inflammatory and will help control 
pain. 

Men and women who have ulcers or bleed- 
ing problems should not take aspirin, but 
most people can take aspirin several 
times a day as long as they drink plenty 
of fluids. Directions should be included 
with the general information given to the 
employees at training. 

It has been determined that for every 
day a person is immobile, it takes 4 days 
to rehabilitate that individual to normal 
function. Therefore, mobility is impor- 
tant. Light duty will prevent the em- 
ployee from behavioral changes. Fur- 
thermore, a person who is at bedrest for 
several weeks becomes weak and is very 
likely to have an injury the first day on 
the job since theri muscle tone is poor. 
Maintenance of muscle strength is very 
critical when the worker must return to a 
job situation (8). Although the majority 
of the injured miners reported in the 
underground coal mining statistics re- 
turned to the job in 3 weeks or less, it 
is important to consider the rapidity of 



the deterioration of strength if a miner 
has been in bed for several days. Physi- 
cal fitness affects the occurrence of 
back injuries, so the injured employees 
should be given instructions in strength- 
ening and stretching exercises and should 
be encouraged to do these before return- 
ing to work (2). 

It follows, therefore, that the person 
who is in poor physical condition may 
have weight and posture problems and 
could be a candidate for an injury. 
Stress may also affect the back, causing 
muscles to tighten which may lead to mus- 
cle spasm. A physical fitness program 
may diminish many of these problems. 

In November 1982, two psychologists 
from North Texas State University con- 
ducted a study involving eight industries 
and approximately 1,500 employees. One 
hour of back injury prevention education 
was provided to the employees of these 
industries. The programs were given in 
small groups at the jobsites and were 
customized for the specific industry and 
their needs. Companies participating in 
the evaluation were representative of 
both light and heavy industry. Both 
safety directors and participants were 
asked to respond. The employee response 
was a random sampling. The results were 
as follows: Safety directors report a 
40-pct reduction in lost-time days the 
year following the presentation with a 
decrease in medical insurance expenses in 
three of the companies. There was an in- 
crease in numbers of reported injuries, 
but those participating in the program 
reported fewer injuries. The partici- 
pants reported an 86-pct decrease in 
lost-time days and a 63-pct reduction in 
injuries. Lawlis and Hennig (_5) reasoned 
that the reported increase in back inju- 
ries was primarily due to the changes of 
management's perception of back injuries 
and the employees' willingness to report 
early injury and accept early treatment. 
The large reduction in lost time would 
support that premise. 

Although each program was customized, 
all employees received the same format of 
information. Followup material included 
posters that were placed in common areas 



85 



and reminder cards placed in paychecks 6 
months following the program. A short 



refresher course was offered 1 yr follow- 
ing the initial presentation. 



CONCLUSIONS 



Back injuries are a major health prob- 
lem in the United States, but can be pre- 
vented and controlled through education 
and training if the material is designed 
for the person on the job. It must 
be informative, interesting, fast-moving, 
and relative. Body mechanics concepts 
must be emphasized in different ways so 
the individual can adopt the positions 
that work best for his or her situation 
both at work and at home (14) . Use of 
the first aid treatment should be encour- 
aged at the first sign of back strain. 
Light-duty programs should be initiated 



to keep the individual mobile and in 
touch with his peers and management. 
Practical demonstration is important, but 
actual participation in sitting, stand- 
ing, lifting, and pivoting procedures is 
essential. The trainer must be well- 
prepared before the employee can be ex- 
pected to retain the information present- 
ed. Followup is a mandatory part of any 
safety program. If employees are given 
appropriate information, they can and 
will take responsibility for their own 
back health care (13). 



REFERENCES 



1. Bergquist-Ullman, M. , and U. Lars- 
son. Acute Low Back Pain in Industry. 
Acta Orthopaedic Scandinavia, Suppl. 170, 
1977, pp. 1-117. 

2. Cady, L. D. Strength and Fit- 
ness and Subsequent Back Injuries in 
Firefighters. J. of Occupational Med., 
V. 21, 1979, pp. 269-273. 

3. Carroll, B. J. An effective Safe- 
ty Program Without Top Managment Sup- 
port. Professional Safety, July 1982, 
pp. 20-24. 

4. Grant, R. E. Massage With Ice in 
the Treatment of Painful Conditions of 
the Musculoskeletal System. Phys. Med. 
Rehab., v. 45, 1964, pp. 223-238. 

5. Lawlis, G. F. , and E. G. Hennig, 
Jr. An Evaluation of Individualized Edu- 
cational Services for the Prevention of 
Industrial Back Injuries Unpublished Pro- 
gram Evaluation for Spine Education Cen- 
ter, Dallas, TX, November 1982; available 
upon request from N. C. Selby, Spine Ed. 
Center, Dallas, TX. 

6. Manuele, F. A. Work Practices 
Guide for Manual Lifting. National Safe- 
ty News, October 1982. 

7. Nachemson, A. L. Low Back Pain — 
Its Etiology and Treatment. Clinical 
Medicine, 1971, pp. 18-23. 



8. Selby, D. K. Conservative Care of 
Nonspecific Low Back Pain. Orthopedic 
Clinics of North America, v. 13, No. 3, 
July 1982, pp. 427-437. 

9. Showman, J. , and L. T. Wedlick. 
The Use of Cold Instead of Heat for the 
Relief of Muscle Spasm. Med. J. of Aus- 
tralia, V. 2, 1964, pp. 612-614. 

10. This, L. Results-Oriented Train- 
ing Design. Training and Dev. J. , June 
1980, pp. 14-22. 

11. Time (Chicago). That Aching Back. 
July 14, 1980, pp. 30-34. 

12. U.S. Mine Safety and Health Admin- 
istration. Injury Experience in Coal 
Mining, 1978-1981. MSHA IR's 1112, 1122, 
1133, 1138. 

13. White, A. H. Conservative Care — 
California. The Challenge of the Lumbar 
Spine, Conference Proceedings, Dallas, 
TX, Dec. 10-12, 1981. 

14. Zemke, R. , and S. Zemke. 30 
Things We Know for Sure About Adult 
Learning. Training/HRD, June 1981, pp. 
45-52. 

15. Zenger, J. The Painful Turnabout 
in Training. Training and Dev. J., De- 
cember 1980, pp. 36-49. 



86 



200 / 




FIGURE 1. - This position will put 200 lb of pressure on the 
back. 



87 




FIGURE 2. - Position showing only 25 lb of pressure on the low bock. 





\ 



I- ■ "^ 

FIGURE 3. - Legs should be used for leverage, not the back 




88 



A MANUAL MATERIALS HANDLING (MMH) TRAINING PROGRAM FOR THE MINING INDUSTRY 

By Daniel J. Connelly 1 

ABSTRACT 



Back injuries have been a continuous 
and increasing problem in the mining 
industry. Accident statistics reveal 
that most back, injuries occur during man- 
ual materials handling activities. Vari- 
ous methods have been attempted to con- 
trol these accidents. Training in safe 



materials handling is one approach that 
has been used over the years. This paper 
provides a number of general recommenda- 
tions and specific examples to assist 
training personnel in the mining industry 
to develop a manual materials handling 
training course to reduce back injuries. 



INTRODUCTION 



Back injuries have been a continuous 
and increasing problem in the mining 
industry (table 1). In coal mining, 
for example, approximately 20 pet of all 
injuries are back injuries. Consequent- 
ly, a significant percentage of the total 
nonfatal lost workdays are due to back 
injuries (table 2). Likewise, the costs 
of back injuries to the mining industry 
are significant. 

A review of accident statistics show 
the majority of back injuries reported by 
the mining industry are the result of ma- 
terials handling accidents (table 3). 
The accident classification, handling 
materials, is defined as an accident re- 

^ Safety specialist, Pittsburgh Research 
Center, Bureau of Mines, Pittsburgh, PA. 



lated to handling packaged or loose ma- 
terial while lifting, pulling, pushing, 
or shoveling (10). 2 

Miners involved in materials handling 
activities, whether underground or on 
the surface, are exposed to a number of 
potential accident situations. Many fac- 
tors contribute to the hazards of ma- 
terials handling. The major components 
are the worker, the task, the materials 
handled, and the work environment. If 
materials are not handled properly, the 
result can be a lost-time injury, most 
likely occurring to the back. 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



TABLE 1. - Total injuries, back injuries, and percentage 
of back injuries at coal, metal, and nonmetal mines 
in the United States, 1978-80 (10-12) 



Coal mines: 

Total Injuries 

Back Injuries 

Back injuries pet, 

Metal mines: 

Total injuries 

Back Injuries 

Back injuries pet, 

Nonmetal mines: 

Total injuries , 

Back injuries 

Back injuries pet. 



1978 



20,203 

3,762 

18.6 

8,713 

1,247 

14.3 

3,844 

664 

17.3 



1979 



23,677 

4,948 

2.9 

9,619 

1,428 

14.8 

3,497 

608 

17.4 



1980 



22,723 

5,111 

22.5 

8,028 

1,246 

15.5 

3,066 

607 

19.8 



1981 



18,821 

4,119 

21.9 

7,570 

1,153 

15.2 

2,697 

461 

17.1 



TABLE 2. - Total nonfatal lost workdays, nonfatal lost workdays 
due to back injuries and percentage at coal, metal and 
nonmetal mines in the United States 1978-80 (1-3) 



89 



1978 



1979 



1980 



1981 



Coal mines: 

Total NFDL , 

NFDL-back injuries , 

Back injuries pet, 

Metal mines: 

Total NFDL 

NFDL-back injuries 

Back injuries pet, 

Nonmetal mines: 

Total NFDL 

NFDL-back injuries 

Back injuries pet 

NFDL Nonfatal days lost. 



494,464 

113,817 

23.0 



148,034 

21,481 

14.5 



78,146 

11,667 

14.9 



662,704 

155,583 

23.5 



187,092 

27,428 

14.7 



75,053 

15,557 

20.7 



662,911 

193,806 

29.2 



179,081 

40,932 

22.9 



58,363 

11,699 

20.0 



616,342 

176,065 

28.6 



149,510 

25,049 

16.8 



58, ,218 

10,521 

18.1 



TABLE 3. - Total back injuries, materials handling' back 
injuries, and percentage at coal, metal, and nonmetal 
mines in the United States 1978-80 (10-12) 



Coal mines: 

Back injuries 

Materials handling back 

injuries 

Back injuries pet. 

Metal mines: 

Back injuries 

Materials handling back 

injuries 

Back injuries ..pet. 

Nonmetal mines: 

Back injuries 

Materials handling back 

injuries 

Back injuries pet. 



1978 



3,762 

2,139 
56.9 



1,247 

636 
51.0 



664 

380 
57.2 



1979 



4,948 

2,932 
59.3 



1,428 

749 
52.5 



608 

386 
63.5 



1980 



5,111 

3,008 
58.9 



1,246 

654 
52.5 



607 

375 
61.8 



1981 



4,119 

2,427 
58.9 



1,153 

597 
51.8 



461 

271 
58.8 



'Handling materials accidents are defined as accidents related 
to handling packaged or loose material while lifting, pulling, 
pushing, or shoveling. 



In addition to back injuries, there are 
other types of injuries associated with 
materials handling accidents. These 
other injuries, such as bruises and cuts 



of the fingers and hands , account for a 
minor percentage of the total costs of 
injuries arising from materials handling. 



90 



WHAT CAN BE DONE? 



In many mining companies, frustrations 
over the seemingly insoluble back injury 
and materials handling problems create 
attitudes that further aggravate the 
problems. Several positive steps can be 
taken to control the hazards. Tradition- 
ally, the prevention of back injuries has 
been attempted by 

1. Careful selection and placement of 
workers. 

2. Training in safe lifting. 



3. Designing the job to fit the worker 

(Z). 

Training for manual materials handling 
in the mining industry is the main topic 
of this paper. Training in safe handling 
methods alone will not solve the back in- 
jury problem. The problems of back inju- 
ries and materials handling are multidi- 
mensional in nature. Training is only 
one approach that should be used in com- 
bination with other control methods, such 
as job redesign, and worker selection and 
placement (1). 



TRAINING TO CHANGE BEHAVIOR 



The ultimate objective of any training 
program is to change behavior of people. 
That is, to cause them to do their jobs 
effectively and correctly (i.e., safely). 
However, there are many factors that in- 
fluence human behavior on the job. Be- 
havioral change can be insensitive to 



training if other factors (i.e., environ- 
mental, managerial, physiological, so- 
cial, etc.) predominate in determining 
the way people are behaving (6). There- 
fore, training can be identified as one 
of many variables to consider and control 
to achieve behavioral change. 



TRAINING TO REDUCE BACK INJURIES 



Training for the purpose of reduc- 
ing back injuries has been conducted 
throughout industry for many years. Even 
though, few in-depth studies have been 
made to determine the effectiveness of 
lifting and materials handling training 
(8^, p. 176). 

The importance of training in manual 
materials handling (MMH) , however, has 



been generally accepted, and is likely to 
continue. What is needed is a clear def- 
inition of what the training should be 
and how it should be taught. The only 
general criteria would appear to be that 
training should involve the worker ac- 
tively in the learning process and iden- 
tify specific techniques and hazards of 
MMH tasks (8, p. 199). 



A MODEL MANUAL MATERIALS HANDLING TRAINING COURSE 



The National Institute for Occupa- 
tional Safety and Health (NIOSH) pub- 
lication, "Work Practices Guide for 
Manual Lifting," provides recommenda- 
tions regarding the training of work- 
ers who perform MMH tasks (_9, pp. 99- 
101). These recommendations form the 
basis for a model MMH training course. 
The aims of safety training in MMH should 
be to — 

1. Make the miners aware of the dan- 
gers in MMH. 



2. Show miners how to avoid unneces- 
sary stress. 

3. Teach miners individually to be 
aware of what they can handle safely. 

The following items should be covered 
in the training course: 



materials han- 



1 . The risks in manual 

dling. Based upon the materials commonly 
handled and the accident history of the 
mine. 



91 



2. The basic principles of manual m at- 
erials handling . The basic physics of 
MMH, the body as a system of levers, and 
the work needed to shift loads. 



3. The effects of MMH. 



The basic 



anatomy of the back, muscles, and joints, 
and the effect of lifting on the body. 

4. Individual awareness of the body's 
strengths and weaknesses . Teach miners 
how to judge the weights they can handle 
safely, and where their body strengths 
and weaknesses lie. 

5. How to avoid accidents . Teach min- 
ers how to recognize and avoid the physi- 
cal factors that might contribute to an 
accident, for example. 



g. Is the floor clean, dry, and 
nonsllp? 

h. Is the area clear where the 
load will be set down? 

6. Handling skill : Emphasize the ac- 
tual materials handled at the mine. Pro- 
vide instruction on the following general 
points: 

a. How to prepare for materials 
handling tasks. 

b. How to recognize what loads can 
be handled safely. 

c. How to keep the load close to 
the body when lifting. 



a. Is the load free to move and 
not stuck? 



d. How to lift without twisting or 
bending sideways 



b. Is it a weight that can be 
safely handled by one person? 

c. Are lifting aids available? 



e. How to use the legs to get 
close to the load and to make use of 
the body weight and the kinetic energy 
of the body and load. 



d. Does the load have handles to 
grasp or can they be provided? 



f. How to develop timing for 
smooth and easy lifting. 



e. Is protective clothing needed? 

f . Is the work area clear of 
obstruction? 



7. Handling aids: Demonstrate the 
handling aids available for materials 
handling tasks, and encourage their use. 



DETERMINING MATERIALS HANDLING TRAINING NEEDS 



The basic steps of training in general 
apply equally well to the training of 
miners for materials handling tasks. In 
order to develop an effective training 
program, identify and define the materi- 
als handling problems and then establish 
procedures to control those problems. 

Information necessary to evaluate ma- 
terials handling Includes accident rec- 
ords, mine conditions, and discussions 
with mine personnel. An accident analy- 
sis will Identify problem areas, in terms 
of the who, what, where, how, and why 
(individuals, tasks, materials handled, 
causes, and so forth). This information 



will provide a good idea of what areas 
or topics need to be emphasized during 
training (_3 ) . 

In addition to the basic Information 
about accidents, obtain specific details 
concerning mine policies, procedures, 
equipment and supplies, and responsibili- 
ties of the miners. Obtaining this in- 
formation will require talking to the 
mine personnel most familiar with the 
day-to-day operation of the mine, the 
section supervisors. Questions should 
cover the problems and hazards of materi- 
als handling activities at the mine or 
sections of the mine. 



92 



HAZARDS OF MATERIALS HANDLING IN THE MINING INDUSTRY 



Accident analyses of materials handling 
accidents have identified several poten- 
tially hazardous tasks (_5 ) . Most of 
these accidents involve the act of manu- 
ally handling materials, specifically, 
lifting and lowering, pushing and pull- 
ing, carrying, and shoveling. Although 
these accidents provide an indication of 
the general hazards of materials han- 
dling, training should concern specific 
tasks and materials associated with the 
problem areas. 

Understandably, the underground mine 
environment is more hazardous and more 
difficult to work in than most surface 
environments. Underground conditions 



increase the potential for accidents. 
For example, poor maintenance of the mine 
floor results in slippery and uneven 
footing which contributes to accidents. 
Bending or sitting on folded legs is com- 
mon in mines of low roof height. Lifting 
or carrying materials under such condi- 
tions can result in back injuries (4). 
In addition, the weight of materials han- 
dled sometimes exceeds the physical capa- 
bility of the miner and this can result 
in injury. It is for these reasons that 
training in materials handling should 
include discussions of the work environ- 
ment and the physical limitations of the 
workers. 



TRAINING METHODS 



Lecturing requires that the instructor 
talks and the miners listen. While this 
method can be effective for a short per- 
iod of time, it should not be the only 
method used. A short lecture on the ba- 
sic structure of the back, for example, 
should be combined with slides or films 
and class discussion. A discussion al- 
lows for class participation. Asking a 
few questions helps to focus on the top- 
ics you want to cover. The following ex- 
amples are questions that can be used for 
discussion: 

1. What are the most common injuries 
and accidents in the mining industry and 
at your mine? 

2. What are the most common materials 
handling accidents? 

3. Where in your mine are materials 
handling accidents occurring? And to 
whom? 



4 . How can 
prevented? 



these 



accidents 



be 



Demonstration is the best teaching 
method to use to show how something is 
done. The classes should be small enough 
that safe materials handling methods 
can be demonstrated, preferably at the 
worksite. The materials or objects known 
to be associated with materials handling 
accidents and back injuries (such as 
trailing cables, oil drums, roof bolts, 
timbers, rock dust bags, etc.), should be 
used in actual demonstrations. 

Mine supervisors should be actively in- 
volved in developing and conducting the 
training course. It does little good to 
train miners in safe handling methods if 
the methods are not used during materials 
handling tasks on the job. Therefore, 
observing day-to-day job performance and 
correcting unsafe acts are essential 
responsibilities of the mine supervisors. 



COURSE OBJECTIVES 



The purpose of the course should be to 

instruct miners in the safe methods of 

materials handling. After completion of 

the course, the miners should be able to 
identify the following: 

The basic anatomy of the back. 



General safety rules. 
Safe lifting method. 
Safe carrying method. 
Safe shoveling method. 



93 



The miners should be given a test to 
demonstrate they have learned the mate- 
rial. The test method should provide 



evidence, either by doing or by listing 
the safe methods, that the miners have 
learned what you want them to do. 



COURSE MATERIALS 



The following illustrations provide ex- 
amples of course materials for training 
in materials handling. 



the training course. Figure 3 shows the 
personal protective equipment that should 
be worn (2). 



A brief lecture on the basic anatomy 
of the back can be used to teach the 
effects of materials handling on the 
body. Figure 1 shows the structure of 
the back (2). The NIOSH publication, 
"Work Practices Guide for Manual Lift- 
ing," provides reference material that 
can be helpful (9). 

Discussions of personal experiences 
with back pain can assist in "selling" 
the need for the training. Examples of 
materials handling accidents at your mine 
"bring home" the point that the potential 
for injury is real. Analysis of your 
mine's accident history can reveal the 
problem areas that need to be emphasized. 
Figure '2 illustrates typical examples of 
materials handling accidents. 

Strains, bruises, cuts, or other inju- 
ries may result from handling materials. 
Personal protection equipment and reasons 
for wearing them should be covered during 



Lifting and lowering materials are the 
most common materials handling tasks per- 
formed in the mines. Figure 4 provides 
examples of safe lifting methods. The 
lifting tasks selected for your training 
course should include the materials most 
often handled at your mine. 

Accident statistics show that handling 
electrical cable is a leading cause of 
back injuries and materials handling ac- 
cidents in mining. Many of these acci- 
dents result from the miner pulling on 
the cable rather than lifting. Figure 5 
provides instruction on the safe handling 
of cable. 

Shoveling coal and rock account for a 
large number of back injuries in mining. 
Therefore, instruction provided on the 
safe method for shoveling materials is 
needed as shown in figure 6 (2^) . The 
main point to stress is to avoid twisting 
the back while shoveling. 



GENERAL MATERIALS HANDLING SAFETY RULES 



There are a number of general safety 
rules that apply to materials handling. 
One of the most important is to plan 
ahead. Determine where the material will 
be placed before moving it. If carrying 
materials a long distance, plan rest 
stops to prevent fatigue. If the materi- 
al required to be moved is too heavy. 



then get help or use a mechanical device, 
such as a hoist, wheelbarrow, front-end 
loader, or forklift. The miner should 
also be instructed to become aware of the 
surrounding environment, obstacles in the 
pathways, and wet or muddy floor 
surfaces. 



SUMMARY 



Back injuries have been identified as a 
significant problem area in the mining 
industry. Accident statistics have shown 
that most back injuries occur during ma- 
terials handling activities. Training in 
safe materials handling methods is one 
approach for control of back injuries. A 
number of general recommendations and 



specific examples have been presented to 
assist training personnel in the mining 
industry to develop a manual materials 
handling training course to reduce back 
injuries. It is hoped that some prac- 
tical suggestions have been made and 
will be used where needed in the mining 
industry. 



94 



REFERENCES 



1. Ayoub, M. M. Control of Man- 
ual Lifting Hazards: I. Training in 
Safe Handling. J. of Occupational Med. , 
V. 24, No. 8, August 1982, pp. 573-577. 



7. Snook, S. H. , R. A. Campanelli, 
and J. W. Hart. Three Preventive Ap- 
proaches to Low Back Injury. Profession- 
al Safety, July 1978, pp. 34-38. 



2. Bituminous Coal Operations Associa- 
tion and National Coal Association. Ma- 
terials Handling (SLIDE/TAPE Training 
Program). Produced by National Photo- 
graphic Laboratories, Inc., Houston, TX, 
1981. 

3. Christopherson, K. I., C. H. Cover, 
and M. J. Klishis. How To Tailor Train- 
ing Material To Fit Your Mine. BuMines 
contract J0188069; for inf., contact W. 
J. Wiehagen, Pittsburgh Res. Center, 
Pittsburgh, PA. 



8. U.S. Department of Health, Educa- 
tion and Welfare NIOSH Report on Interna- 
tional Sjnnposium: Safety in Manual Mate- 
rials Handling (State Univ. NY at Buffa- 
lo, July 18-20, 1976). Pub. as Safety in 
Materials Handling, ed. by C. G. Drury, 
NIOSH Pub. 78-185, 219 pp.; NTIS PB- 
297-660. 

9. U.S. Department of Health and Hu- 
man Services. Work Practices Guide for 
Manual Lifting. NIOSH Pub. 81-122, 1981, 
183 pp.; NTIS PB 82-178-948. 



4. Diaz, R. A., and A. D. Chitaley. 
System For Handling Supplies in Under- 
ground Coal Mines. BuMines contract 
H0188049; for inf., contact G. R. Bock- 
osh, Pittsburgh, Res. Center. 

5. Foote, A. L. , and J. S. Schaefer. 
Mine Materials Handling Vehicle (MMHV) 
contract H0242015, MB Associates). Bu- 
Mines OFR 59-80, 1978, 308 pp.; NTIS 
PB 80-178890. 

6. Nertney, R. J., and J. R. Buys. 
Training as Related to Behavioral Change. 
ERDA-76-45-6, SSDC-6, June 1976, 9 pp.; 
available from System Safety Development 
Center, Idaho Falls, ID. 



10. U.S. Mine Safety and Health Admin- 
istration. Injury Experience in Coal 
Mining, 1978-1981, MSHA IR's 1112, 1122, 
1133, 1138. 



11. . Injury Experience in Me- 
tallic Mineral Mining, 1978-1981. MSHA 
IR's 1116, 1126, 1137, 1142 



12. 



Injury Experience in Non- 



metallic Mineral Mining (except stone and 
coal), 1978-1981. MSHA IR's 1114, 1124, 
1135, 1140. 



95 



Your back is a "complex System" 



It includes : 



THE SPINE 

33 bones (vertebrae). The upper 
24 are separated by disks that act 
as cushions. 



NERVES 



31 pairs branching out from the 
spinal cord, sending information 
to the brain and orders to the 
muscles. 




MUSCLES 

400 of them producing motion in 
all directions, they are attached to 
the bone by about 1,000 tendons. 



THE SPINAL CORD 
A half-inch thick "cable" of nerves, 
about 18-inches long, controls all 
activities below neck level. 



FIGURE 1. - Basic anatomy of the back. 



96 







^-^^^ 





FIGURE 2. - Examples of materials handling accidents. 



97 



METATARSAL SHOES 

Injuries to the feet are common and painful. 
They most frequently occur when materials that 
are being carried slip or when they fall be- 
cause they are stacked improperly. Metatarsal 
shoes are recommended because they protect 
your entire foot — the toes, the arch, and 
the top. 




HARD HATS 

It is easy to bump your head against overhead 
obstacles or stacked supplies while working in 
congested, dark surroundings. Hard hats are 
essential for your protection and should be 

worn at all times whether you're working 

outside or inside the mine. 




SAFETY GLASSES 

Your eyes should be protected from cool dust, 
rock dust and other particles that can cause 
severe irritations. Safety glasses make sure 
such damaging abrasives do not enter your 
eyes. 




LEATHER GLOVES 

When handling materials and supplies, it is im- 
portant to maintain a firm grip. Leather gloves 
help you to do this, as well as protecting your 
hands from cuts, burns, and blisters that could 
become infected. 




RUBBER BOOTS 

Since you will be working around high voltage 
trolley wires and wet, muddy areas it may be 
necessary to wear rubber boots to avoid any 
electrical shock. Rubber boots also help you 
maintain a firm foothold. 




LEG BANDS 

Securing your pants legs is an essential part 
of your safety. Leg bands is one way of doing 
this. You should wear them at all times to a- 
void tripping and getting caught on moving 
pieces of equipment. 




FIGURE 3. - Personal protective equipment. 



98 




As you approach the load determine 
its weight, size and shape. Consider 
your physical ability. 




Bend the knees and get a firm grasp 
on the object. 




Do not twist or turn until the object 
is in carrying position. 




Stand close to the object with feet 
8 to 12 inches apart for good bal- 
ance. 




D 

Using both leg and back muscles lift 
the load straight up. Keep the ob- 
ject close to the body. 




Rotate body by turning your feet and 
make sure path of travel is clear. 




To set the object down, use leg and 
back muscles and lower the object 
by bending the knees. 



FIGURE 4. = Safe lifting. 



the fic 



99 



B 



First, stand close to the belt and 
establish firm footing. 



Then get the items to the side of 
the belt by pulling gradually, without 
sudden jerky movements. 



Lift the items off the belt, keeping 
your back as straight as possible and 
holding the load close to your body. 



Remember not to twist your back 
when unloading materials, as this 
miner is doing. Instead, reposition 
your feet, and turn your body. 





First, be sure to wipe off any dirt or 
grease before reaching for the ob- 
ject you are going to lift. 



B . Then, stand close to the object and 
get a firm foothold. 



Straddle the load sonnewhat and squat 

down, bending at the knees not 

at the back. 



Incorrect d. 






Hold the object securely so your grasp 
does not slip. 




E . Finally.. ..slowly straighten to an up- 
right stance, keeping your back in a 
vertical position. 



E. Then bend your knees to lower the load. 




FIGURE 4. - Safe lifting. -Continued, B, From a belt; C, an irregular shaped object. 



100 







FIGURE 5. - Handling cable. 



101 



Always shovel in the direction the belt is 
moving . This way, you avoid catching 
the shovel in the belt and keep from 
getting hit with the handle. 




Avoid twisting your back. Turn your feet 
and your entire body so your back is not 
strained. 




FIGURE 6. - Example of safe shoveling. 



102 



MECHANIZATION OF MATERIALS HANDLING TASKS 
By Richard L. Unger"! 



ABSTRACT 

The Bureau of Mines is sponsoring re- materials handling activities are dis- 
cussed. A daily supply handling system 
is presented, as well as several concepts 
to reduce manual handling requirements 
during equipment and mine maintenance. 



search aimed at reducing the manual ef- 
fort required to transport or transfer 
materials used in underground coal mines. 
Specifically, production supply, mine 
maintenance, and equipment maintenance 



INTRODUCTION 



In the mid-1970' s, the Bureau of Mines 
sponsored studies to determine the types 
and causes of materials handling injuries 
in underground coal mines. One result of 
this work was the determination that ap- 
proximately one-half of all materials 
handling accidents occur in the produc- 
tion supply function (fig. 1). Produc- 
tion supply refers to the handling of 
daily supply items from the surface to 
locations near the working face in sup- 
port of production activities. Examples 
of this type of handling include trans- 
porting rock dust bags, roof bolts, and 
timbers. It was also found that the com- 
bination of equipment and mine mainte- 
nance functions accounted for approxi- 
mately one-quarter of the materials han- 
dling accidents. Some examples of these 
functions include extracting motors from 



continuous miners, 
hanging cable. 



changing tires, and 



The Bureau initiated two research proj- 
ects to reduce the need for manual han- 
dling of items through a systems approach 
involving mechanization of supply han- 
dling. The first project, begun in 1978, 
was to develop a system for handling 
daily supplies in underground coal mines, 
directed primarily toward the production 
supply function. The second project was 
to develop a vehicle for mine and equip- 
ment maintenance activities. These two 
Bureau research projects were aimed at 75 
pet of the materials handling accidents 
in underground coal mines. This paper 
describes the methods and results to date 
of these two projects. 



A SYSTEMS APPROACH TO HANDLING DAILY SUPPLIES 



The surest way to reduce materials han- 
dling injuries is to reduce or eliminate 
the need for manual handling. This is 
the purpose of the Bureau's daily supply 
handling system. Studies conducted at a 
Pennsylvania coal mine over a 2-yr span 
indicate that production times could be 
increased by at least 3 pet and supply 
handling injuries reduced by as much as 
7 3 pet if a supply system based on pal- 
letization and mechanical handling were 
to be implemented. Such a system has 
been developed and is outlined below. 

^Civil engineer, Pittsburgh Research 
Center, Bureau of Mines, Pittsburgh, PA. 



PALLETIZATION 

Daily supplies would be palletized on 
the surface and moved as unit loads 
throughout the mine. As much as possi- 
ble, pallets of supplies as delivered by 
vendors would be moved to the section. 
The supplies moved to the section would 
be based on the estimated needs for that 
day. This should eliminate delay or lost 
production time owing to lack of materi- 
als or waste due to oversupply. Large 
items, such as timbers or rail, would be 
left on dedicated supply cars or trailers 
off the haulageway. These items are then 
off-loaded as needed. Empty pallets. 



railcars, and trailers are returned to 
the surface on the return supply trip. 

PERMISSIBLE FORKLIFT 

Once the supply trip brings the pallets 
to the section, a method is required for 
off-loading and delivering them to the 
face as they are needed. After consider- 
ing many alternatives, the Bureau chose 
the idea of a permissible, battery- 
powered forklift, with a winch and forks, 
for handling pallets and long narrow 
items such as timbers. An additional 
benefit would be using the forklift as a 
hoist to assist in equipment maintenance 
by reversing the forks. Figure 2 gives 
the forklift's specifications while fig- 
ures 3 through 7 present its layout. 2 
The forklift offers compactness, maneuv- 
erability and ease of materials handling 
underground. Forklifts are commonly used 
to handle supplies in the surface yard, 
however, the underground applications 
have usually been limited to high-seam 
mines that allow permissible diesel ve- 
hicles. This appears to be due to the 
unavailability of suitable forklift ve- 
hicles for use in the lower seams. Elec- 
tric cable forklifts are available for 
underground use; but the cable restricts 
reach and maneuverability, thereby limit- 
ing its suitability for the section han- 
dling operations needed for this system^ 
(fig. 8). 



103 



The forklift's task would be to unload 
the supply trip and move the pallets to 
the section storage area. As supplies 
are needed at the face, the forklift 
would deliver them pallet by pallet up to 
their point of use. The forklift's small 
size would enable it to manuever around 
most equipment in the entry, such as a 
roof bolter. 

Rails, timber, and pipe are carried by 
a special sling attachment on the side of 
the forklift directly to the usage point 
(fig. 7). The forklift's operation gen- 
erally requires two people: the operator 
and a helper who spots loads and directs 
pallet movement. 

When not being used to handle supplies , 
the forklift has uses in equipment and 
mine maintenance activities. By revers- 
ing the forks, a hydraulically powered 
hoist is created that can remove or posi- 
tion heavy motors or lift timber to sup- 
port the roof. It should be pointed out, 
however, that the main function of the 
forklift is supply handling. This dif- 
fers from other vehicles sometimes used 
to handle supplies, such as a scoop. 
Often, when a scoop is needed to handle 
supplies, it is being used for its pri- 
mary task of coal cleanup. The supplies 
must then be moved by other means, usual- 
ly by hand. 



TEST RESULTS 



The daily supply handling system was 
tested at the Safety Research Coal Mine 
located at the Pittsburgh (PA) Research 
Center. Overall, the system worked well, 
with the need for manual handling of 
items reduced to the initial loading 
of the pallets and final use. However, 
there were problems , such as 

Pallet design. Some wooden pallets 
could not withstand the rugged under- 
ground conditions, and broke apart after 
a short time in use. 

^Diaz, R. A., and A. D. Chitaley. Sys- 
tem for Handling Supplies in Underground 
Coal Mines. BuMines contract H0188049; 
for inf., contact G. R. Bockosh, Pitts- 
burgh Res. Center, Pittsburgh, PA. 



A few lightweight-design steel pallets 
were tested and proved to be much stur- 
dier. More testing is needed in this 
area. 

The permissible forklift, though work- 
ing well for a prototype, has a few defi- 
ciencies that need to be corrected. 
These include the need for increased 
traction in soft ground, greater overall 
battery life and speed, and more precise 
handling. The Bureau is considering a 
second prototype to correct these prob- 
lems. An alternative solution would be 
for the mining industry or equipment man- 
ufacturer to apply their expertise in 
this area. 

-^Work cited in footnote 2. 



104 



The palletization-f orklif t method of 
handling daily supplies in underground 
coal mines shows great promise for re- 
ducing manual materials handling. The 



results should be a reduction in materi- 
als handling injuries, more efficient 
distribution of supplies, as well as sav- 
ings in daily supply handling labor. 



MECHANICAL DEVICES FOR MINE MAINTENANCE AND EQUIPMENT MAINTNENACE 



As stated earlier, production sup- 
ply, mine maintenance, and equipment 
maintenance accounted for approximately 
75 pet of materials handling accidents 
reported in Bureau's studies. The Bu- 
reau's work into a system for handling 
daily production supplies resulted in 
a palletization-f orklif t scheme. This 
section discusses the Bureau's project to 
reduce mine maintenance and equipment 
maintenance accidents. 

The initial intent of this project was 
to design and develop a universal mainte- 
nance and materials handling vehicle. 
This approach has been tried before by 
the Bureau with poor results. 4 In a 
sense, the permissible forklift for the 
daily supply handling system is another 
attempt at an underground materials han- 
dling vehicle. However, there are two 
main differences between the forklift and 
the vehicle proposed for this project. 

1. The forklift has one major task; 
transporting pallets. A maintenance ma- 
terials handling vehicle, on the other 
hand, should be adaptable to individual 
tasks and be able to transport and posi- 
tion a variety of single items into all 
areas of the mine. This requires a ver- 
satile vehicle with several lifting and 
carrying attachments. 

2. The forklift is intended to carry 
large volumes of items on a daily basis. 
A maintenance materials handling vehicle 
would be used only in specific situa- 
tions, and therefore with less frequency. 
This would make the vehicle harder to 
justify in terms of cost. 

^Foote, A^ L. , and j! si Schaefer. 
Mine Minerals Handling Vehicle (MMHV) 
(contract H0242015, MB Associates). Bu- 
Mines OFR 59-80, 1978, 308 pp.; NTIS PB 
80-178890. 



Based on the above reasons, it was de- 
cided that a series of simple, relatively 
inexpensive materials handling devices 
would be more readily accepted by mining 
industry. Each device would be tested in 
work situations at cooperating mines. 
The results of the tests, as well as 
plans and guidelines on fabrication, 
would be made available to the industry. 
The hope is that individual mining com- 
panies can be made aware of how mechani- 
zation of mine and equipment maintenance 
tasks can be both inexpensive and helpful 
in reducing their materials handling 
problems. 

Eight materials handling device-tool 
concepts were generated, based on acci- 
dent statistics, interviews with mine op- 
erators and underground mine visits. 
This lift was then reduced, due to budget 
constraints, to what was felt to be the 
five most useful devices. These devices 
are briefly described below. 5 

Lifting Boom (fig. 9) . One of the ma- 
jor needs identified was for a simple 
boom device that could be used to lift 
and transport components weighing up 
to 1 ton and to lower them safely to 
the ground. The boom would mount on the 
front of a small scoop when the bucket 
was removed, and would have a hydraulic 
winch with 100 ft of cable. 

A device was built on this concept and 
is now in one of the demonstration mines 
for testing. All comments from the mine 
thus far have been favorable. 

^Conway, E. J., and W. W. Elliot. Mine 
Maintenance Material Handling Vehicle: 
Investigative Study and Concept Develop- 
ment, BuMines contract H0 113018; for 
inf., contact E. A. Ayres, Pittsburgh 
Res. Center, Pittsburgh, PA. 



105 



Mine Jack-Wheel Changer (fig. 10) . 
Another concept is for a floor type jack 
that could be used to lift a component, 
transport it over short distances, and 
maneuver it into position for installa- 
tion. Typical tasks would be aligning 
and lifting a drive motor under the fen- 
der of a shuttle car, or changing wheels 
weighing up to 1,000 lb on shuttle cars, 
cutters, etc. 



Mud Truck (fig. 12) . This device is 
designed for use in low-seam mines. It 
is equipped with high flotation tires to 
permit one person to pull it through soft 
bottoms. The steerable front tires and 
articulation joint provide even load dis- 
tribution with maximum maneuverability. 
It can be used for transporting toolbox- 
es, parts, and supplies to wherever they 
are needed. 



The lift capability is derived from a 
hydraulic jack mechanism. The jack head 
tilts and rotates to allow more flexibil- 
ity in placing the load. The ballon 
tires make movement easier over the mine 
floor, and the long handle provides lev- 
erage by which to maneuver the load up, 
down, or sideways as required. 

Cable Puller (fig. 11) . This device is 
a capstan powered by either a hydraulic 
or electrical source, and pulls a rope 
attached to a mining vehicle trailing ca- 
ble. The pull rate can be controlled by 
the tension held by the laborer. The 
capstan can pull trailing cable and water 
hose out of an entry when preparing to 
move across the section or pull any cable 
on a conventional mining section. 



Pivot Crane (fig. 13) . This portable 
winch crane is an adaptation of devices 
commonly used on vehicles above ground. 
The crane mounts in a socket strategical- 
ly located on any machine and can be 
stored at the section shop when not in 
use. Its uses include major component 
replacement in the 100- to 2,000-lb cate- 
gory or any lifting task adjacent to a 
machine. 

All of these devices can be fabricated 
at the mine or in a small shop. Most can 
be modified to fit the needs of a partic- 
ular mine. For instance, a chain winch 
can be substituted for the hydraulic 
winch in the lifting boom, at a substan- 
tial cost saving. 



DISCUSSION 



It is hoped that the mining industry 
will incorporate the ideas the Bureau is 
presently pursuing in relation to reduc- 
ing materials handling accidents. Though 
every mine is unique, with its own par- 
ticular materials handling problems, the 
ideas presented in this paper are adapta- 
ble to any mine in one form or another. 



It is up to the mine operator to make 
sure that avoidable materials handling 
accidents are eliminated by providing the 
most efficient methods of supply distri- 
bution as well as reasonable amounts 
of mechanization of materials handling 
tasks. 



106 



140 
130 
120 
110 
100 

(O 

z 90 

UJ 

o 

o 80 

o 

< 

li. 70 



133 (50%) 



'a 



'a 



44 ( 16%) 



27(10%) 

171 



30(11%) 



^ 



35(13%)- 



i 









r 



^^v 



FIGURE 1. - AccicJent frequenciesfordifferent 
handling functions. 



Permissibility 


MSHA and Pennsylvania approved for work-face 


Type 


Battery powered skid steer 


Drive 


4 wheels driven by two hydraulic motors 


Payload 


3- by 3-ft pallets typical at maximum 1,500 lb 




Timber 16 ft by 7 by Sin, quantity 3 to 5 


Speed 


1.3 mph moximum 


Ronge 


2 h continuous duty 


Dimensions 


Height 56- in over canopy 




Width 61 in 




Length 12 ft, 4 in 




Ground clearance 7, 9, or II in 




Forks 31 -in long by 38 travel 




Empty weight 7,470 lb 


Auxiliary 


Power winch 3,000-lb copacify 


equipment 


l/4-in-diam wire rope, 




120ft 




Timber carrying hooks 




Reversible forks 




Sheove and hook attachment for crane use of forks 



FIGURE 2. - The underground supply handling 
forklift specifications. 



56-in, 
3- post canopy 



Hydraulic pump 
l5-hp,dc motor 



Starter 



Hydraulic tank 



Telescopic mast 



126-v, 200- Ah 
battery 




31-in forks by 38-in travel, 
lO-in lift without raising mast 



am control joystick 
Forklift controls 
Light switch box 

-Power winch, dog clutch, 
and control lever 



7-in or 9-in 
ground clearance 



-6:50 by 10 
pneumatic tires 



FIGURE 3. - Perspective schematic-underground supply handling forklift. 



107 



Joystick tram control-) p Panic stop bar 

e extinguisher 



l5-hp,dc motor 



Battery 



3l-in by 38-in travel, 
side shift carriage forklift 




Hydraulic tank 



6:50 by 10 tires- 
FIGURE 4. - Top view schematic — underground supply handling forl<lift. 



Telescopic mast 
with 3° forward 



15-hp, 
dc motor _ 2-stage 

hydraulic pump 



126-v, 200-Ah 
battery- 




Hydraulic 
orbital motor 



FIGURE 5. - Front and right side view schematics— underground supply handling forklift. 



108 



Arms fold back for storage 



// ^ 



^3E^ 



i}! 



Side of machine 



J 




Sling coble 



rl6-ft-|onq timbers 



' /^//, 



IglMM! 



7-in minimum , ; - i i -^ — ■■ — i-i-. 



FIGURE 6. - Sling arrangement for carrying 
long, narrow loads. 




FIGURE 7. - Hoist configuration of forks. 
18-ft entry 




Skid steer 
turning center 



Crib set 



"^c^=? 



^r 



FIGURE 8. - Maneuvering capabilities of skid steer. 



109 




4^ 



FIGURE 9. - Lifting boom during tests at a low-seam coal mine. 



no 



Slide mechanism 



^^ 



-Balloon tire 



Tiltable saddle 



Telescoping 
handle, 

_fi, Y_ 



To laborer , 



Control 




Trailing cable 



Motor 

PLAN VIEW 



-ri n r. 




^Foot pad 

SIDE VIEW 

FIGURE 10. • Mine jack-wheel changer. 



Capstan 



Anchor chain. 




Drive chain 



Skid mounted' 



SIDE VIEW 

FIGURE 11. . Cable puller. 



Roof 



, Load deck 



Steer and tow bar^ 




SIDE VIEW 

FIGURE 12. - Mud truck. 



Machine frame. 




Component-. 






"Swivel crane 



)r 



Socket 



Floor 
FIGURE 13. - Pivot crane. 



TiU.S. GOVERNMENT PRINTING OFFICE: 1983-605-015/50 



INT.-BU.OF mines, PGH., pa. 27100 



963 



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